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<div>==General information on Gemology==<br />
<br />
===What is Gemology?===<br />
<br />
'''Gemology''' is the scientific study of gemstones, which often involves the study of mineralogical fundamentals such as formations, genesis, localities, physical properties and identification of gemstones. It includes the basic knowledge of structural, crystallographic, chemical and physical characteristics and properties of gems. It also involves the way in which gemstones are fashioned.<br />
<br />
''Special Gemology'' deals with categories and varieties of gemstones, synthetic stones and imitations. Conventionally, the organic substances such as amber, pearls, coral and the non-minerals are also included in this subject of special gemology.<br />
<br />
''Practical Gemology'' refers to the application of the knowledge of characteristics and properties of gemstones in identification or separation of synthetics and imitations. Diamond grading is included in practical gemology.<br />
<br />
===What is a Gemologist?===<br />
<br />
A gemologist is someone who studies gemstones. Being recognized as a gemologist usually involves having credentials from one of the Institutes for Gem(m)ological Studies discussed below (see '''Becoming a Gemologist''' below).<br />
<br />
===What are gemstones?===<br />
<br />
Gemstones are usually [[mineral]]s but sometimes [[organic | <SPAN title=" derived from a living organism " class="popup">organic</SPAN>]] substances.<br />
What separates them from minerals in general is that they are used in jewelry or for ornamentation. That is a very thin line of separation, but usually we take 4 factors into account:<br />
<br />
* [[Durability]]<br />
* [[Rarity]]<br />
* [[Beauty]]<br />
* [[Acceptability]]<br />
<br />
And, of course, there is a 5th factor:<br />
<br />
* [[Fashion]] <br />
<br />
All the factors above are relative in nature. For instance, [[amber]] has very poor durability, isn't very rare and in general is not highly priced. Yet it is considered to be a gem due to its beauty.<br />
<br />
On the other hand, most [[sapphire]] has good durability but can be very unattractive and inexpensive. Only a small portion of all sapphires mined have good color/beauty. The same can be said for [[diamond]]; the vast majority of diamonds mined are used for industrial purposes because they lack the necessary beauty to be worn as jewelery.<br />
<br />
==Becoming a Gemologist==<br />
<br />
Becoming a gemologist in general means hard work and commitment. A wise teacher once said "You are only permitted to read books related to our trade and a religious book of your choice from now on . . . for the rest of your life".<br />
<br />
===Education===<br />
<br />
Although you can find very useful information on the Internet (like here), we '''strongly''' suggest that you take formal training from one of the established institutes listed below. Our editors have graduated from at least one of them.<br />
<br />
Some of the online gemological schools are basicaly run by one person and in case of mishap the school will cease to exist, aswell will be your "diploma".<br />
<br />
====Gem-A====<br />
<br />
Better known as The Gemmological Association and Gem Testing Laboratory of Great Britain, this school is London based with departments worldwide. It offers distance tutoring as well as teaching centers.<br><br />
The primary focus is on in-depth theory and the exams are the hardest to take in the industry. A fellowship of Gem-A means esteem. <br />
<br />
Costs:<br />
<br />
Foundation correspondence course GBP 1035.00<br><br />
Diploma correspondence course GBP 1410.00 (on completion is granted the FGA title).<br />
<br />
Gem Diamond diploma course GBP 1650.00 (on completion is granted the DGA title).<br />
<br />
Website http://gem-a.info/<br />
<br />
====GIA====<br />
<br />
The Gemological Institute of America is the most prestigious and respected institute for gemology within the United States. Its main location is in Carlsbad, California, with facilities in New York and Los Angeles. Courses may be completed by distance learning via the online "virtual campus".<br />
It was established in 1931 by Robert Shipley, and currently the GIA is the world’s largest and one of the most respected nonprofit institutes of gemological research and learning internationally.<br />
It employs nearly 900, including scientists, diamond graders, and educators.<br />
<br />
Costs:<br />
<br />
On campus (CB/NY/LA): 6 month continuous program (780 hours) $14,695<br />
<br />
Distance Education: GEM130, GEM230, GEM230L, GEM120, GEM220,GEM220L, GEM240, GEM240L (Maximum completion time: 63 months) $6,975 ($7,420 International)<br />
<br />
What you earn: Graduate Gemologist Diploma, Graduate Diamonds Diploma, Graduate Colored Stones Diploma<br><br />
Website: http://www.gia.edu<br />
<br />
====AIGS====<br />
Thailand is in the heart of Southeast Asia's gem and jewelry production and trading area. It presents you with an extraordinary opportunity to learn gemology in theory and practice while experiencing the gem business in a three dimensional way. <br />
<br />
The A.G. program, which leads to the A.G. (Accredited Gemologist) Diploma, includes the four core courses:<br> <br />
:E102: Gem Identification<br><br />
:E103: Diamond Grading and Pricing<br><br />
:E201: Colored Stone Grading and Pricing<br><br />
:E301: Synthetic and Treated Gem Identification. <br />
<br />
These 4 courses can be studied in any order, in one or several study periods at AIGS. It is recommended that “Gem Identification” be studied before “Synthetics and Treated Gems”. <br />
<br />
Students enrolling in the entire A.G. program are entitled to a 15% discount off the total tuition fee. Courses must be taken within one year of the first date of payment. Beyond the one year period, students will be subjected to any tuition increases that may have occurred. (Example: Old fee = 20,000 Baht, New fee in effect since date of enrollment = 22,000 Baht, Additional amount to be paid = 2,000 Baht.)<br />
<br />
Living expenses and general overhead are amazingly low compared to countries such as USA, Japan and most of Europe. Students studying at the AIGS can live with a US$600 to US$1000 budget per month including housing near the school, weekend field trips, restaurants and entertainment. Of course, you can spend much more if you want to, but this amount yields a comfortable lifestyle!<br><br />
Website: http://www.aigsthailand.com/<br />
<br />
====DGemG====<br />
The Deutsche Gemmologische Gesellschaft (The Educational Training Center of the German Gemmological Association) is located in Idar-Oberstein, Germany. Idar-Oberstein is an international colored stone gem capital, where gem cutting has been traditionally mastered for centuries. It is currently bustling with local gem artists and studios. It has, perhaps, the highest per capita population of gem cutters in the world! The German Gemmological Association was founded in 1932.<br />
Its laboratories have modern state of the art equipment, and one of the most extensive colored and exotic gemstone collections available.<br />
<br />
Costs:<br />
<br />
Euro 5,800.00 <br><br />
<br />
Website:http://www.dgemg.de/gemmologen_eng/index.php?seite=home<br />
<br />
====FGAA====<br />
<br />
The Gemmological Association of Australia (GAA), founded in 1945, is Australia’s historic trade-accepted non-profit educational authority for gemology. <br><br />
They offer gemological courses in 6 state divisions.<br />
<br />
Costs: contact one of the six state divisions for pricing.<br />
<br />
Website: [http://www.gem.org.au www.gem.org.au]<br />
<br />
====CGA====<br />
<br />
The Canadian Gemmological Association, based in Toronto Canada, is a Canada-wide professional organization which has set the standard for excellence in the practice of gemology. It was founded in 1958 by Dean S.M. Field, and has since provided training in gemology to persons dealing with gemstones in the jewelery industry and to hobbyists for better appreciation and possible new career opportunities within gemology.<br />
<br />
They offer a one-year correspondence course as well classes on location.<br />
<br />
Costs:<br />
<br />
The two-year correspondence course, leading to a Diploma in Gemmology and a Fellowship (FCGmA) in the Canadian Gemmological Association, is offered from CAD 2,150.00<br />
<br />
Website [http://www.canadiangemmological.com/ canadiangemmological.com]<br />
<br />
===Post Graduate===<br />
<br />
After gaining your gemological diploma, the real fun starts. You will know the basics and more importantly you will know how to understand the many articles published in various [[periodicals]].<br><br />
If you keep up as a consumer of the gemological literature and are involved with continuing education, you will be a good gemologist one day.<br />
<br />
====Career Opportunities====<br />
<br />
As with any profession, it is all up to you what you will become and what your salary will be.<br />
<br />
Think of a gemological diploma as if you have finished your first year in college and the pay rate according to that when you start out. You will be qualified to find jobs in gemological laboratories worldwide and will be the key figure in the local jewelry store. You may become manager of a company, start your own gem trading business, become an appraiser, or you might just stay shoveling municipal gardens etc. Anything you set your mind to. Pay rate is according to experience and market.<br /><br />
Our best advice is to start networking from the start and to seek a new employer every few years so you can gain as much know-how as you can.<br />
<br /><br />
<br />
<br /><br />
'''Next: [[Glossary_of_Terms| Glossary of Terms]]''' or<br />
<br /><br />
'''[[Origins_of_minerals| Origins of Minerals]]'''<br />
<br /><br /><br />
'''[[Table_Of_Contents| Return to the Table of Contents]]'''</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Glossary_of_Terms&diff=7839Glossary of Terms2009-05-30T23:03:40Z<p>Anatase: </p>
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<div>'''absorption spectrum''': the pattern of dark and light bands that is seen when a gem is observed with a [[spectroscope]]. These bands result from the absorption of certain wavelengths of white light passing through the stone. The colors that are NOT absorbed determine the color of the gem.<br />
<br />
'''acicular''': crystals that have a "needle-like" form; such as rutile in [[quartz]].<br />
<br />
'''[[Sheen#Iridescence | Adularescence]]''': a billowing flow of whitish or bluish colors that seem to float along the surface; caused by the diffused reflection of light from parallel intergrowths of albite and orthoclase [[feldspar]].<br /> <br />
{{tooltip|Moonstone adularescence|images/b/b4/Moon-adul.JPG|Show me}}<br />
<br />
'''allochromatic''': a gemstone is allochromatic when it is colorless in its pure state. Subsequent color is derived from an impurity (usually a metallic oxide) that is not an essential part of the mineral's chemical composition. [[Beryl]], [[quartz]] and [[corundum]] are all examples of allochromatic gemstones.<br />
<br />
'''anisotropic''': a term for crystals that are doubly refractive, which means that they will break light into 2 different rays, traveling at different speeds within the crystal.<br />
<br />
'''[[Sheen#Asterism | asterism]]''': star-like phenomenon caused by light reflecting from tiny fiber-like inclusions that are perpendicular to the crystal faces; the number of rays depends on the cut of the gem in concert with the orientation of the inclusions.<br /> {{tooltip|Asterism|images/1/15/Stars.jpg|Show me}}<br />
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'''biaxial''': term used to describe crystals with two directions of single refraction. These are minerals crystallizing in the [[orthorhombic]], [[monoclinic]] and [[triclinic]] crystal systems<br />
<br />
'''birefringence''': double refraction; the difference between the minimum and maximum [[refraction|refractive index]] of a gem (although strictly birefringence we should name that "maximum birefringence")<br />
<br />
'''botryoidal''': interlocking, rounded masses that sometimes look like grapes or bubbles resulting from radiating masses of fibrous crystals.<br /> <br />
{{tooltip|Botryoidal Malachite|images/f/f4/Botry-sm.JPG|Show me}}<br />
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'''bruting''': The cutting of one diamond with another. It is only used in the production of round stones, in order to round out the girdle of the diamond on a lathe<br />
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'''cabochon''': A type of gemstone cut where the back of the stone is flat (or slightly domed) and the top is formed as a smooth rounded dome.<br /> {{tooltip|Cabochon|images/e/e0/Emeraldcab.JPG|Show me}}<br />
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'''carat''':a unit of weight: 1/5th of a gram. The name comes from the seed of the carob tree, which was used as a weight due to its seeds' remarkable uniformity.<br />
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'''[[Sheen#Chatoyancy | chatoyancy]]''': the cat’s-eye-like phenomenon caused by light reflecting from tiny fiber-like inclusions within a gem. The "eye" is seen at right angles to the direction of the inclusions. Stones must be cut en cabochon to see this effect.<br /><br />
{{tooltip|Chatoyancy|images/d/d9/Crysoberyl.jpg|Show me}}<br />
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'''cleavage''':<br />
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'''contact zone''': the area where intruding magma or hot water contacts, alters and recrystallizes the pre-existing surrounding rock<br />
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'''color zoning''' <br />{{tooltip|Color Zoning|images/c/c3/Zoning.jpg|Show me}}<br />
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'''cryptocrystalline''': a term originally used to describe a mineral made up of "sub microscopic components". It is rarely used today since microscopes have become so sophisticated "sub microscopic components" no longer exist. [[Microcrystalline]] is a better description.<br />
<br />
'''crystal''': a solid possessing an orderly and defining arrangement of atomic structure, influencing its physical form and optical properties<br />
<br />
'''[[Crystal_Systems|crystal axes]]''': imaginary reference lines used to determine the relative position of crystal faces<br />
<br />
'''[[Crystal_Systems|crystal systems]]''': the seven main systems into which crystals are divided<br />
<br />
'''crystallography''': the study of crystals and their structure<br />
<br />
'''cubic system''': one of the crystal systems; composed of 6 square faces at 90° angles to each other. Also known as isometric. See [[Crystal Systems & Forms]]<br /> {{tooltip|Cubic System|images/a/a1/Xl_cubic.gif|Show me}}<br />
<br />
'''dichroism''': differential selective absorption seen in some doubly refractive gemstones when viewed in different crytallographic directions<br />
<br />
'''dichroscopes''': instrument used by gemologists to test for pleochroism<br />
· London dichroscope<br />
· calcite dichroscope <br />
<br />
'''double refractive''': all crystals, except cubic, have the ability to split light into two rays when it enters. These 2 rays travel at different velocities. This is termed double refraction.<br />
<br />
'''emission lines''': <br />
<br />
'''epigenetic inclusions''': inclusions that form after the gemstone finished crystallization. If the conditions the crystal is in changes (the heat and/or pressure), material held in solid solution can be forced out and crystallized. Oriented rutile is an an example. Also, secondary cavities can form when fractures in stones are healed. In the process, characteristic patterns of many tiny crystals or negative crystals are formed. <br />
<br />
'''facet''': When used as a noun, a ''facet'' is a flat surface (one of many) cut into a piece of gem rough in order to maximize the reflection of light out of the stone. When used as the verb ''to facet'', it means to cut a gemstone into a faceted shape, such as a round brilliant cut, emerald cut, cushion cut or similar. <br />{{tooltip|Faceted citrine|images/b/b6/Table-facet.jpg|Show me}} <br />
<br />
'''[[Luminescence#Fluorescence | fluorescence]]''': the emission of visible light by a gemstone when exposed to a light source whose light we normally cannot see. When the gemstone is exposed to ultraviolet light (UV), which falls outside the range of light that we can see, the UV light is absorbed by the gemstone. Due to processes inside the gemstone, it will lose energy. This loss of energy causes the UV light to change to a color in the visible light range (red, orange, yellow, green, blue, indigo or violet).<br />
<br />
'''hexagonal system''': one of the crystal systems; having three axes equal in length at 120° to each other, with the C or vertical axis at 90° to the other axes. See [[Crystal Systems & Forms]].<br /> {{tooltip|Hexagonal system|images/e/ec/Xl_hexagonal.gif|Show me}}<br />
<br />
'''idiochromatic''': A gemstone is idiochromatic when the element causing its color is an essential part its chemical composition. For example, iron, which is an intrinsic part of the chemical makeup of [[peridot]], is the cause of its green color.<br />
<br />
'''inert''': having no change, movement, or reaction. In chemistry, the term inert is used to describe something that is not chemically active.<br />
<br />
'''[[Origins_of_minerals#Igneous_.28Magmatic.29_rocks | igneous rocks]]''': rocks that formed at very high temperatures from siliceous (silica rich) melts. <br />
<br />
'''imitations''': materials used to mimic a gemstone without having the same composition as the stone it is imitating. Example: synthetic color-changing sapphire used to imitate alexandrite; cubic zirconia used to imitate diamond.<br />
<br />
'''impurities''': elements in the crystal structure that are foreign to the basic chemical composition of the gem. <br />
<br />
'''inclusions''': crystals, liquid- or gas-filled cavities that have been enclosed within a gem or mineral. Often peculiarly diagnostic in determining the identity of a gemstone. Example: bysollite inclusions in [[demantoid]] garnet.<br />{{tooltip|Horsetail inclusions|images/8/85/Horsetail.gif|Show me}}<br />
<br />
'''infrared light''': Also known as heat, these wavelengths are beyond the visible red: between 790nm and 1,000,000nm on the electromagnetic spectrum. These radiations can produce a reaction with some gems and minerals. See [[luminescence]] and [[thermoluminescence]].<br />
<br />
'''interference figure''': the figure seen when anisotropic gemstones are viewed in convergent polarized light. This figure may be diagnostic in determining the identity of a gemstone.<br />
<br />
'''isometric system''': another name for the ''cubic system''.<br />
<br />
'''isomorphous replacement''': replacement of elements in a mineral's composition by other elements with the same valency. These elements do not substantially alter the crystal structure of the gem but can cause wide variations in the gem's optic and physical properties. The garnet group is an excellent example of isomorphic replacement.<br />
<br />
'''isotropic''': gems and minerals that are singly refractive. This means that light that enters the medium travels as one ray at one velocity in all directions. All cubic gems and amorphous substances are isotropic. See [[anisotropic]]. <br />
<br />
'''karat''': the measure used to describe the purity of gold. 24 karat is pure gold, 100% or 24 of 24 parts gold; 18 karat is 75% gold, or 18 parts gold and 6 parts alloy metals; 14 karat is 58% gold, or 14 parts gold with 10 parts alloy metals. <br />
<br />
'''[[Sheen#Iridescence | labradorescence]]''': the phenomenon displayed by [[labradorite]] (caused by lamellar formation of lattice structure), which has an appearance of a predominantly bluish or greenish oil slick on water <br /><br />
{{tooltip|Labradorescence|images/7/79/Labrador.jpg|Show me}}<br />
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'''marble''': a metamorphic rock created when a certain type of limestone is subjected to tremendous heat and pressure.<br />
<br />
'''massive''': used to describe crystals that have no apparent crystal form or are masses of smaller crystals.<br />
<br />
'''[[Origins_of_minerals#Metamorphic_rocks | metamorphic rock]]''': igneous or sedimentary rocks that have been altered or recrystallized by extreme heat or pressure. <br />
<br />
'''microcrystalline''': <br />
<br />
'''monoclinic system''': one of the crystal systems; all axes sides meet at 90°, with all the axes being of different lengths. Two of the axes are prependicular, with the other situated at 90° to them. See [[Crystal Systems & Forms]].<br />{{tooltip|Monoclinic system|images/1/13/Xl_monoclinic.gif|Show me}}<br />
<br />
'''opalescence''': a reflection of a milky or pearly light from a gem's interior, sometimes used as a synonym for irridescence.<br />
<br />
'''optic character''': a stone's property of being either isotropic, uniaxial or biaxial; found by determining how the light travels down crystal axes; common instruments used to determine optic character are polariscope and conoscope<br />
<br />
'''optical interference figure''': see [[interference figure]]<br />
<br />
'''optic sign''': Uniaxial and biaxial gems can be further subdivided as being optically positive or negative. In uniaxial gems, if the refractive index value of the extraordinary ray is greater than the ordinary ray, the gem is positive and vice versa. In a biaxial gem, if the intermediate refractive index value is closer to the higher value, it is positive; if closer to the lower value, negative. Examples: Quartz is uniaxial positive; topaz is biaxial positive. <br />
<br />
'''orange peel''': a surface appearance resembling the outer skin of an orange. This is sometimes seen in plastic and glass similants and should be observed in reflected light.<br />
<br />
'''orthorhombic system''': one of the crystal systems; three axes all meet at 90° to each other, with all the axes being of different lengths. See [[Crystal Systems & Forms]].<br /> {{tooltip|Orthorhombic system|images/a/a0/Xl_orthorhombic.gif|Show me}}<br />
<br />
'''pegmatite''': an igneous rock, rich in quartz and feldspar with very large grains, indicating slow cooling<br />
<br />
'''phantom crystal''': also known as "ghost crystal", they occur in quartz when there is an interruption in the growth cycle. It appears like a faint crystal within a crystal<br />
<br />
'''pleochroism''': the appearance of more than one color (usually when viewed with a dichroscope) as a function of the crystallographic direction from which one is viewing a gem. It is caused by the selective absorption of the ordinary and extraordinary rays in uniaxial gems (dichroism) and, in biaxial gems, by the selective absorption in the 3 principal vibrational directions of the crystal (trichroism). <br />
<br />
'''polarized light''': light that is vibrating in one direction only. Doubly refractive gems polarize light into 2 rays which travel at right angles to each other.<br />
<br />
'''protogenetic inclusions''': inclusions that form BEFORE the gem. The gem crystal traps the inclusion as it grows. Burmese rubies from Mogok often exhibit protogenetic inclusions. <br />
<br />
'''refractive index''': The degree that light is bent when it enters a stone. This is measured with a refractometer. Most gems have refractive indices that range between 1.43 and 1.98. Diamond has a refractive index of 2.42, which means it bends light 2.42 times more than air!<br />
<br />
'''rock''': a geological unit made up of one or more minerals. The properties of rocks can vary widely depending on the varying percentages of minerals in their makeup<br />
<br />
'''rough''': a gemstone in its brute state, before undergoing cutting or carving <br /><br />
{{tooltip|Scapolite rough|images/a/a0/Scapolite_rough.JPG|Show me}}<br />
<br />
'''schist''': a metamorphic rock containing layers of different minerals that can be described as foliated or fissile.<br />
<br />
'''[[Origins_of_minerals#Sedimentary_rocks | sedimentary rock]]''': rocks composed as the result of weathering and erosion of pre-existing rocks. Wind, water, and frost are able to wear away the highest mountains and the hardest rock masses, redepositing them in lakes, rivers and oceans, where they compact and form new rocks.<br />
<br />
'''selective absorption''': property of absorbing a particular selection of the wavelengths of white light as they pass through a stone. If all wavelengths of light pass through a stone evenly, it appears colorless. If the stone absorbs all wavelengths equally, it appears black. If it absorbs certain wavelengths and reflects all others, it will appear opaque and colored. If it absorbs certain wavelengths and transmits all others, it will appear transparent and colored.<br />
<br />
'''singly refractive''': means that a light ray will pass through a crystal as one ray, not split or polarized; isotropic stones (cubic system) are all singly refractive<br />
<br />
'''spectroscopy, absorption''': a technique (using a spectroscope) of measuring how much light of a particular wavelength (color) is absorbed by a gemstone. Color is often related to the presence of a particular element. Absorption spectroscopy is an inexpensive way to test for the presence of elements within a gem.<br />
<br /> {{tooltip|Spectrum|images/4/44/SmDiffraction_spectrum_scale.jpg|Show me}}<br />
<br />
'''spot reading method''': finding the refractive index of a cabochon cut stone by finding where the light in the refractometer appears as half light/half dark on the reading scale <br /> {{tooltip|Spot Reading|images/e/e3/Spotreadingsmall.JPG|Show me}}<br />
<br />
'''strain/interference colors''': evidence of internal strain that appears as rainbow-like colors (primarily reds and oranges) under a polariscope<br />
<br />
'''syngenetic inclusions''': inclusions that form simultaneously with the gemstone. The gem grows at varying rates, forming enclosed cavities that can be filled with solids, liquids or gases or combinations. <br />
<br />
'''synthetics''': Man-made gemstones having the same physical and chemical composition as the natural gemstones. Lab grown.<br />
<br />
'''table''': the flat top of a faceted stone<br /><br />
{{tooltip|Triangular table facet|images/b/b6/Table-facet.jpg|Show me}}<br />
<br />
'''tetragonal system''': one of the crystal systems; three axes meeting at 90°, with the C axis being longer than the A and B axis (which are the same length). See [[Crystal Systems & Forms]].<br /> {{Tooltip|Tetragonal system|images/f/f3/Xl_tetragonal.gif|Show me}}<br />
<br />
'''trade name''': the name given to a gemstone usually for marketing purposes, ie: tanzanite for ziosite, Tashmarine &trade; for diopside, mandarine garnet for spessartite.<br />
<br />
'''trichroic''': anisotropic stones that may display three colors; a type of pleochroism<br />
<br />
'''triclinic system''': one of the crystal systems; all the axes are different lengths, with no angles meeting at 90°. See [[Crystal Systems & Forms]].<br /> {{tooltip|Triclinic system|images/8/8b/Xl_triclinic.gif|Show me}}<br />
<br />
'''trigonal''': one of the crystal systems that is considered by some gem references to be a subsystem of the hexagonal system. A trigonal prism has the effect of being a three sided prism. See [[Crystal Systems & Forms]].<br /> {{tooltip|Trigonal system|images/3/35/Xl_trigonal1.gif|Show me}}<br />
<br />
'''twinning''': when two or more crystals of the same species grow together during the formation period; can interlock or grow from the edge outward. Shows a "venetian blind" effect under magnification<br />
<br />
'''ultraviolet light (UV)''': energy in wavelengths too short to be seen by the human eye, beyond the visible violet, measuring 100 to 380 nanometers. Some gemstones, when exposed to UV, emit colors very bright and different from their normal colors. SWUV light is harmful to the eyes so protective goggles should be worn.<br />
<br />
'''uniaxial''': the optic character of anisotropic minerals, meaning they have one direction of single refraction: Tetragonal, trigonal and hexagonal crystals are uniaxial.<br />
<br />
'''white light''': light consisting of all colors and wavelengths<br />
<br /><br />
<br />
<br /><br />
'''Next:[[Origins_of_minerals| Origins of Minerals]]'''<br />
<br /><br /><br />
'''[[Table_Of_Contents| Return to the Table of Contents]]'''</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=10x_Loupe&diff=783810x Loupe2009-05-30T22:53:39Z<p>Anatase: </p>
<hr />
<div>After the eye and the brain, the 10x Loupe (or "hand lens") is the instrument most used by gemologists.<br /><br />
It is used to inspect the interior and exterior of a gemstone, and is the primary instrument used for clarity grading of Diamonds. <br />A good 10x Loupe can be bought for under USD 50.00 and a gemologist should carry it with her/him at all times.<br />
<br />
It is recommended that you buy a loupe with a matte black casing around the lenses to prevent reflections. Golden and chromed casings may look nice, but they can interfere with colors.<br />
<br />
[[Image:B&L.jpg|right|framed|10x Loupe with black casing around the lenses]]<br />
<br />
==About lenses==<br />
<br />
Lenses used in optics are usually made of crown and flint glass.<br /><br />
Crown glass has a refractive index between 1.5 and 1.6 and is low dispersive, while flint glass may have higher refraction indices and is highly dispersive. Both types work complementary and are widely used in gemological loupes.<br />
<br />
Lenses are cut in different shapes (convex, concave and combinations) following Coddington Shape factors for best form. This is to eliminate spherical and chromatic aberrations, which would distort the image. <br /><br />
The best forms, however, do not eliminate the aberrations completely, therefore several lenses (two or three) are cemented together for optimum performance. These are named compound lenses. The "doublet" loupes have 2 lenses while the "triplet" loupes have 3 lenses of various shapes cemented together.<br />
<br />
==Magnification==<br />
<br />
The 10x means that the loupe will magnify an image 10 times, so if a 1mm<sup>2</sup> square will appear to be 1cm<sup>2</sup>.<br />
<br />
Gemological loupes come in different magnifications (from 3x up to 30x) and with different fields of view. For everyday use, a 10x triplet lens with a large field of view (25.4mm) is your best choice. The higher magnification ones usually have a smaller working distance (the distance between the loupe and the gemstone).<br /><br />
The standard 10x loupe has a working distance of about 2.5 cm, while a 20x loupe will have a 1.25 cm working distance.<br />
<br />
You can measure what the working distance for you is by the following formula:<br />
<br />
:<math> Working\ distance = \frac{least\ distance\ of\ focus}{10}</math><br />
<br />
The "least distance of focus" is different for every person. You can measure it by holding a ruler next to your eye (pointing away from you and the zero position lined up with your eye), then place the nail of your thumb (from the other hand) close in front of your eye. Close your other eye.<br /><br />
You will notice that the nail is out of focus. Now slowly slide your thumb along the ruler until the nail of your thumb is in sharp focus. Read the value of the ruler where the focus is full and that is your personal "least distance of focus". For me, the original author of this section, that was at 17cm, so my working distance is 1.7 cm.<br />
<br />
Although one might expect that a 20x loupe will give a better view of the item being examined, that is only the case for experienced users and only then after having first examined the object with a 10x lens. The reason for this is that the higher the magnification, the lesser your field of view and the lesser the margin of focus.<br /><br />
With a 10x lens you will have an average working distance of about 2.5 cm with some margin below and before. Although the focus outside your working distance is not optimal, you can still see the area reasonably well.<br /><br />
For a 20x loupe, those margins are all half and it will be extremely difficult to see "the big picture", causing you to miss an inclusion in a stone completely. Therefore use the 20x hand lens only in addition to the 10x loupe for a closer inspection.<br />
<br />
Another good reason for using a 10x loupe is that it is the standard in clarity grading for Diamonds.<br />
<br />
==Chromatic aberration==<br />
<br />
[[image:chromaticaberration.jpg|left]]<br />
<br />
<br />
Chromatic aberration refers to color fringing of the image due to dispersion inside the glass lens. The outer edges of the lens refract the most and hence more dispersion will occur from light rays at those points.<br />
<br />
To overcome this, two lenses (one bi-concave and one bi-convex) of different dispersive powers (crown and flint glass) are placed side by side.<br /><br />
Loupes that are corrected for chromatic aberration are named "achromatic".<br />
<br />
<br clear=all /><br />
<br />
==Spherical aberration==<br />
<br />
[[image:sphericalaberration.jpg|right]]<br />
<br />
<br />
Lenses also suffer from spherical distortion, also caused by differences in refraction on the outer edges from the lens and the rays which travel through the center. This results in a hazy and out of focus view.<br /><br />
<br />
Correction can be achieved by adding a lens with different curves (like a plano-convex lens) in the loupe. A spherical corrected loupe is called "aplanic".<br /><br />
When the loupe is both aplanic and achromatic, we name it "apochromatic".<br />
<br />
<br clear=all /><br />
<br />
==Doublet loupe==<br />
<br />
[[image:doubletloupe.jpg|frame|left|Two lenses "doublet"]]<br />
<br />
<br />
Doublet loupes consist of two lenses (hence the name "doublet"). The lenses are either corrected for chromatic aberration (achromatic) or spherical aberration (aplanic). In the image to the left two lenses (one bi-concave and one bi-convex) are placed close after each other and cemented together, which will correct the chromatic aberration (achromatic).<br /><br />
When two lenses are used where each lens has a different curvature (concavo-convex or plano-convex), it is an aplanic or othoscopic loupe.<br />
<br />
These loupes are relatively inexpensive (under USD 10.00) and should best not be used in gemology for reasons outlined earlier.<br />
<br />
<br clear=all /><br />
<br />
==Triplet loupe==<br />
<br />
[[image:tripletloupe.jpg|frame|right|Three lenses "triplet"]]<br />
<br />
<br />
The triplet loupe consists of three lenses cemented close together. In the image on the right you see three lenses that make up a triplet loupe (other configurations are possible). From left to right they are:<br />
* A plano-convex lens to eliminate the spherical aberration<br />
* A bi-concave lens<br />
* A bi-convex lens<br />
The latter two overcome the chromatic aberration. All three together they form an apochromatic loupe. This is the loupe you will need as a gemologist.<br />
<br />
<br clear=all /><br />
<br />
==Testing of the loupe==<br />
<br />
You can test your loupe for chromatic aberration by looking at a white light source through your loupe. If the image remains white (also on the outer edge) it will be achromatic.<br /><br />
Spherical aberration can be tested on mm squared drawing paper. The squares should remain square in the total view of your loupe.<br />
<br />
==Proper use of the 10x loupe==<br />
<br />
[[Image:Loupe.jpg|left|thumb|175px|Proper use of the loupe]]<br />
<br />
<br />
In order to be successful working with the hand lens, one must practice with it first.<br /><br />
Unfold the loupe and hold the lens casing between index finger and thumb. Place the lens just before your eye (or just before your spectacles), letting the back of your thumb rest against the side of your nose to keep the loupe steady.<br /><br />
The three remaining fingers should be parallel with or just below your index finger.<br />
<br />
With your other hand, hold an object and bring it in front of the lens. To steady the object, let the thumb of the hand that holds the object rest against the middle finger of the hand that holds the loupe.<br />
Manipulate the object in a wiggly motion while keeping the thumb and middle finger in contact. Practice this with several objects until you get a feel for the loupe.<br /><br />
From there on you can exercise with gemstones held in tweezers to explore external and internal features in gemstones. When you find yourself on hands and knees searching for stones that popped out of the tweezers, don't be alarmed. All gemologists have red knees.<br />
<br />
To keep your eyes from strain, try to keep both eyes open, the unused eye staring blank.<br />
<br clear=all /><br />
<br />
==Related topics==<br />
<br />
* [[Microscope]]<br />
<br />
==Sources==<br />
<br />
* ''Gemmology Third Edition'' 2005 - Peter G. Read ISBN 0750664495<br />
* ''Gem-A'' Foundation notes<br />
* ''Gem Identification Made Easy'' 3th edition (2006) - A. C. Bonanno, Antoinette Matlins<br />
<br /><br />
<br /><br />
'''Next: [[Spectroscope| Spectroscope]]'''<br />
<br /><br /><br />
'''[[Table_Of_Contents| Return to the Table of Contents]]'''</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=The_Chemistry_of_Gemstones&diff=1602The Chemistry of Gemstones2006-03-07T02:50:43Z<p>Anatase: /* Electronic Configuration of Atoms */</p>
<hr />
<div>An '''element''' is a substance that can not be seperated into a simpler form of matter by ordinary means. An element may be a solid, liquid or a gas. <br><br />
Some common elements are carbon, gold, copper, iron, oxygen, silicon, etc.<br />
<br><br />
An '''atom''' is the smallest part of an element. It is the smallest, indivisible particle of a chemical element. Each atom consists of negatively charged electrons and positively charged protons. There are a similar number of electrons and protons to produce an electrically neutral atom. An atom can not be subdivided by any chemical process.<br />
[[Image:atom.gif]]<br><br />
=Electronic Configuration of Atoms=<br />
Properties of an element, chemical compounds and the formation of crystals depends a great deal on the disposition of electrons and their interaction. The electrons circle the nucleus in all directions, like a cloud. The radius of the average of their movements, is defined as a shell or energy level. These shells will remain at a predictible level which is determined by quantum mechanics. Each shell contains only a given number of electrons. There is a maximum of 2 in the innermost shell (known as the k shell), and 8 each in the second and third shells (known as the l and the m shells respectively). There are 18 each in the next two shells (known as the n and the o shells) and 32 in the next full p shell.<br />
<br />
=Atomic Number=<br />
Each of the chemical elements is made up of like atoms, also known as the atomic number. They all have the same number of protons. Hydrogen (atmoic No. 1), has one proton and one planetary electron. The heaviest naturally occurring atom, uranium, has 92 protons and 92 electrons.<br><br />
Element 112 was discovered on 9th February 1996 in Darmstadt, Germany. The identified isotope currently is the heaviest atom ever produced by man and has an atomic mass of 277, that is, 277 times heavier than hydrogen. <br><br />
Except for hydrogen, all the other nuclei of atoms contain neutrons, varying from 2 in the case of helium to 146 in the uranium atom. The '''atomic weight''' of an element is the weight of the protons and neutrons, which form the nucleus of the atom. If an atom gains or loses one electron, it ceases to be electrically neutral and becomes what is known as an ion. The gaining of electrons, produces a negatively charged ion, known as an anion. Loss of electrons results in a positively charged ion referrred to as a cation.<br />
<br />
=Molecules=<br />
Atoms of elements can combine together to form tiny fractions of new substances. These are known as compounds. A molecule is defined as the smallest fraction of a substance, consisting of two or more elements, chemically combined together, which define a substance's composition and chemical properties.<br />
=Valency=<br />
The valency of an element is determined by the number of its atoms which will combine with, or replace, one atom of hydrogen. It can be observed that some elements will have different valencies in different compounds. For example, the compound FeO (ferrous oxide) is divalent and Fe2O3 (ferric oxide) is trivalent.<br />
=Isomorphism & Isomorphic Replacement=<br />
When two ions are brought together, there is a distance where a force of repulsion abruptly sets in and resists any closer approach. It is convenient to consider the ions as "spheres" in contact, and the distance betweeen their centers is taken as the sum of the radiis of the two ions. An anion, such as an oxygen ion, have large ionic radii, where cations have radii that are much smaller.<br />
<br><br />
The common cations which enter the structure of crystals are often those with similar sized radii, and can replace each other within the structure without unduly straining the space lattice. This accounts for the phenomenon of isomorphism and isomorphic replacement.<br />
<br><br />
In the garnet and spinel groups, magnesia (MgO) and ferrous oxide (FeO) replace one another extensively. Likewise, alumina (Al2O3) and ferric oxide (Fe2O3) can easily replace each other within a crystal's lattice. When such a replacement takes place there can be a a significant variation in chemical composition, without much effecting the internal structure. This accounts for the fact that in certain gemstones of the same species, the specific gravity and refractive indices are not constant specimen to specimen. In some species like garnet, spinel, tourmaline, and beryl the values for refractive index and specific gravity can vary within wide parameters. This is an important factor to keep in mind when testing gemstones.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=The_Chemistry_of_Gemstones&diff=1592The Chemistry of Gemstones2006-03-05T23:09:15Z<p>Anatase: /* Isomorphism & Isomorphic Replacement */</p>
<hr />
<div>An '''element''' is a substance that can not be seperated into a simpler form of matter by ordinary means. An element may be a solid, liquid or a gas. <br><br />
Some common elements are carbon, gold, copper, iron, oxygen, silicon, etc.<br />
<br><br />
An '''atom''' is the smallest part of an element. It is the smallest, indivisible particle of a chemical element. Each atom consists of negatively charged electrons and positively charged protons. There are a similar number of electrons and protons to produce an electrically neutral atom. An atom can not be subdivided by any chemical process.<br />
[[Image:atom.gif]]<br><br />
=Electronic Configuration of Atoms=<br />
Properties of an element, chemical compounds and the formation of crystals depends a great deal on the disposition of electrons and their interaction. The electrons circle the nucleus in all directions, like a cloud. The radius of the average of their movements, is defined as a shell or energy level. These shells will remain at a predictible level which is determined by quantum mechanics. Each shell contains only a given number of electrons. There is a maximum of 2 in the innermost shell (known as the k shell), and 8 each in the second and third shells (known as the l and the m shells respectively). There are 18 each in the next two shells (known as the N and the o shells) and 32 in the next full p shell.<br />
<br />
=Atomic Number=<br />
Each of the chemical elements is made up of like atoms, also known as the atomic number. They all have the same number of protons. Hydrogen (atmoic No. 1), has one proton and one planetary electron. The heaviest naturally occurring atom, uranium, has 92 protons and 92 electrons.<br><br />
Element 112 was discovered on 9th February 1996 in Darmstadt, Germany. The identified isotope currently is the heaviest atom ever produced by man and has an atomic mass of 277, that is, 277 times heavier than hydrogen. <br><br />
Except for hydrogen, all the other nuclei of atoms contain neutrons, varying from 2 in the case of helium to 146 in the uranium atom. The '''atomic weight''' of an element is the weight of the protons and neutrons, which form the nucleus of the atom. If an atom gains or loses one electron, it ceases to be electrically neutral and becomes what is known as an ion. The gaining of electrons, produces a negatively charged ion, known as an anion. Loss of electrons results in a positively charged ion referrred to as a cation.<br />
<br />
=Molecules=<br />
Atoms of elements can combine together to form tiny fractions of new substances. These are known as compounds. A molecule is defined as the smallest fraction of a substance, consisting of two or more elements, chemically combined together, which define a substance's composition and chemical properties.<br />
=Valency=<br />
The valency of an element is determined by the number of its atoms which will combine with, or replace, one atom of hydrogen. It can be observed that some elements will have different valencies in different compounds. For example, the compound FeO (ferrous oxide) is divalent and Fe2O3 (ferric oxide) is trivalent.<br />
=Isomorphism & Isomorphic Replacement=<br />
When two ions are brought together, there is a distance where a force of repulsion abruptly sets in and resists any closer approach. It is convenient to consider the ions as "spheres" in contact, and the distance betweeen their centers is taken as the sum of the radiis of the two ions. An anion, such as an oxygen ion, have large ionic radii, where cations have radii that are much smaller.<br />
<br><br />
The common cations which enter the structure of crystals are often those with similar sized radii, and can replace each other within the structure without unduly straining the space lattice. This accounts for the phenomenon of isomorphism and isomorphic replacement.<br />
<br><br />
In the garnet and spinel groups, magnesia (MgO) and ferrous oxide (FeO) replace one another extensively. Likewise, alumina (Al2O3) and ferric oxide (Fe2O3) can easily replace each other within a crystal's lattice. When such a replacement takes place there can be a a significant variation in chemical composition, without much effecting the internal structure. This accounts for the fact that in certain gemstones of the same species, the specific gravity and refractive indices are not constant specimen to specimen. In some species like garnet, spinel, tourmaline, and beryl the values for refractive index and specific gravity can vary within wide parameters. This is an important factor to keep in mind when testing gemstones.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=The_Chemistry_of_Gemstones&diff=1591The Chemistry of Gemstones2006-03-05T23:08:13Z<p>Anatase: /* Atomic Number */</p>
<hr />
<div>An '''element''' is a substance that can not be seperated into a simpler form of matter by ordinary means. An element may be a solid, liquid or a gas. <br><br />
Some common elements are carbon, gold, copper, iron, oxygen, silicon, etc.<br />
<br><br />
An '''atom''' is the smallest part of an element. It is the smallest, indivisible particle of a chemical element. Each atom consists of negatively charged electrons and positively charged protons. There are a similar number of electrons and protons to produce an electrically neutral atom. An atom can not be subdivided by any chemical process.<br />
[[Image:atom.gif]]<br><br />
=Electronic Configuration of Atoms=<br />
Properties of an element, chemical compounds and the formation of crystals depends a great deal on the disposition of electrons and their interaction. The electrons circle the nucleus in all directions, like a cloud. The radius of the average of their movements, is defined as a shell or energy level. These shells will remain at a predictible level which is determined by quantum mechanics. Each shell contains only a given number of electrons. There is a maximum of 2 in the innermost shell (known as the k shell), and 8 each in the second and third shells (known as the l and the m shells respectively). There are 18 each in the next two shells (known as the N and the o shells) and 32 in the next full p shell.<br />
<br />
=Atomic Number=<br />
Each of the chemical elements is made up of like atoms, also known as the atomic number. They all have the same number of protons. Hydrogen (atmoic No. 1), has one proton and one planetary electron. The heaviest naturally occurring atom, uranium, has 92 protons and 92 electrons.<br><br />
Element 112 was discovered on 9th February 1996 in Darmstadt, Germany. The identified isotope currently is the heaviest atom ever produced by man and has an atomic mass of 277, that is, 277 times heavier than hydrogen. <br><br />
Except for hydrogen, all the other nuclei of atoms contain neutrons, varying from 2 in the case of helium to 146 in the uranium atom. The '''atomic weight''' of an element is the weight of the protons and neutrons, which form the nucleus of the atom. If an atom gains or loses one electron, it ceases to be electrically neutral and becomes what is known as an ion. The gaining of electrons, produces a negatively charged ion, known as an anion. Loss of electrons results in a positively charged ion referrred to as a cation.<br />
<br />
=Molecules=<br />
Atoms of elements can combine together to form tiny fractions of new substances. These are known as compounds. A molecule is defined as the smallest fraction of a substance, consisting of two or more elements, chemically combined together, which define a substance's composition and chemical properties.<br />
=Valency=<br />
The valency of an element is determined by the number of its atoms which will combine with, or replace, one atom of hydrogen. It can be observed that some elements will have different valencies in different compounds. For example, the compound FeO (ferrous oxide) is divalent and Fe2O3 (ferric oxide) is trivalent.<br />
=Isomorphism & Isomorphic Replacement=<br />
When two ions are brought together, there is a distance where a force of repulsion abruptly sets in and resists any closer approach. It is convenieent to consider the ions as "spheres" in contact, and the distance betweeen their centers is taken as the sum of the radiis of the two ions. An anion, such as an oxygen ion, have large ionic radii, where cations have radii that are much smaller.<br />
<br><br />
The common cations which enter the structure of crystals are often those with similar sized radii, and can replace each other within the structure without unduly straining the space lattice. This accounts for the phenomenon of isomorphism and isomorphic replacement.<br />
<br><br />
In the garnet and spinel groups, magnesia (MgO) and ferrous oxide (FeO) replace one another extensively. Likewise, alumina (Al2O3) and ferric oxide (Fe2O3) can easily replace each other within a crystal's lattice. When such a replacement takes place there can be a a significant variation in chemical composition, without much effecting the internal structure. This accounts for the fact that in certain gemstones of the same species, the specific gravity and refractive indices are not constant specimen to specimen. In some species like garnet, spinel, tourmaline, and beryl the values for refractive index and specific gravity can vary within wide parameters. This is an important factor to keep in mind when testing gemstones.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=The_Chemistry_of_Gemstones&diff=1590The Chemistry of Gemstones2006-03-05T23:07:23Z<p>Anatase: /* Atomic Number */</p>
<hr />
<div>An '''element''' is a substance that can not be seperated into a simpler form of matter by ordinary means. An element may be a solid, liquid or a gas. <br><br />
Some common elements are carbon, gold, copper, iron, oxygen, silicon, etc.<br />
<br><br />
An '''atom''' is the smallest part of an element. It is the smallest, indivisible particle of a chemical element. Each atom consists of negatively charged electrons and positively charged protons. There are a similar number of electrons and protons to produce an electrically neutral atom. An atom can not be subdivided by any chemical process.<br />
[[Image:atom.gif]]<br><br />
=Electronic Configuration of Atoms=<br />
Properties of an element, chemical compounds and the formation of crystals depends a great deal on the disposition of electrons and their interaction. The electrons circle the nucleus in all directions, like a cloud. The radius of the average of their movements, is defined as a shell or energy level. These shells will remain at a predictible level which is determined by quantum mechanics. Each shell contains only a given number of electrons. There is a maximum of 2 in the innermost shell (known as the k shell), and 8 each in the second and third shells (known as the l and the m shells respectively). There are 18 each in the next two shells (known as the N and the o shells) and 32 in the next full p shell.<br />
<br />
=Atomic Number=<br />
Each of the chemical elements is made up of like atoms, also known as the atomic number. They all have the same number of protons. Hydrogen (atmoic No. 1), has one proton and one planetary electron. The heaviest naturally occurring atom, uranium, has 92 protons and 92 electrons.<br><br />
Element 112 was discovered on 9th February 1996 in Darmstadt, Germany. The identified isotope currently is the heaviest atom ever produced by man and has an atomic mass of 277, that is, 277 times heavier than hydrogen. <br><br />
Except for hydrogen, all the other nuclei of atoms contain neutrons, varying from 2 in the case of helium to 146 in the uranium atom. The '''atomic weight''' of an element is the weight of the protons and neutrons, which form the nucleus of the atom. If an atom gains or loses one electron, it ceases to be electrically neutral and becomes what is known as an ion. the gaining of electrons, produces a negatively charged ion, known as an anion. Loss of electrons results in a positively charged ion referrred to as a cation.<br />
<br />
=Molecules=<br />
Atoms of elements can combine together to form tiny fractions of new substances. These are known as compounds. A molecule is defined as the smallest fraction of a substance, consisting of two or more elements, chemically combined together, which define a substance's composition and chemical properties.<br />
=Valency=<br />
The valency of an element is determined by the number of its atoms which will combine with, or replace, one atom of hydrogen. It can be observed that some elements will have different valencies in different compounds. For example, the compound FeO (ferrous oxide) is divalent and Fe2O3 (ferric oxide) is trivalent.<br />
=Isomorphism & Isomorphic Replacement=<br />
When two ions are brought together, there is a distance where a force of repulsion abruptly sets in and resists any closer approach. It is convenieent to consider the ions as "spheres" in contact, and the distance betweeen their centers is taken as the sum of the radiis of the two ions. An anion, such as an oxygen ion, have large ionic radii, where cations have radii that are much smaller.<br />
<br><br />
The common cations which enter the structure of crystals are often those with similar sized radii, and can replace each other within the structure without unduly straining the space lattice. This accounts for the phenomenon of isomorphism and isomorphic replacement.<br />
<br><br />
In the garnet and spinel groups, magnesia (MgO) and ferrous oxide (FeO) replace one another extensively. Likewise, alumina (Al2O3) and ferric oxide (Fe2O3) can easily replace each other within a crystal's lattice. When such a replacement takes place there can be a a significant variation in chemical composition, without much effecting the internal structure. This accounts for the fact that in certain gemstones of the same species, the specific gravity and refractive indices are not constant specimen to specimen. In some species like garnet, spinel, tourmaline, and beryl the values for refractive index and specific gravity can vary within wide parameters. This is an important factor to keep in mind when testing gemstones.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=The_Chemistry_of_Gemstones&diff=1589The Chemistry of Gemstones2006-03-05T23:05:21Z<p>Anatase: /* Electronic Configuration of Atoms */</p>
<hr />
<div>An '''element''' is a substance that can not be seperated into a simpler form of matter by ordinary means. An element may be a solid, liquid or a gas. <br><br />
Some common elements are carbon, gold, copper, iron, oxygen, silicon, etc.<br />
<br><br />
An '''atom''' is the smallest part of an element. It is the smallest, indivisible particle of a chemical element. Each atom consists of negatively charged electrons and positively charged protons. There are a similar number of electrons and protons to produce an electrically neutral atom. An atom can not be subdivided by any chemical process.<br />
[[Image:atom.gif]]<br><br />
=Electronic Configuration of Atoms=<br />
Properties of an element, chemical compounds and the formation of crystals depends a great deal on the disposition of electrons and their interaction. The electrons circle the nucleus in all directions, like a cloud. The radius of the average of their movements, is defined as a shell or energy level. These shells will remain at a predictible level which is determined by quantum mechanics. Each shell contains only a given number of electrons. There is a maximum of 2 in the innermost shell (known as the k shell), and 8 each in the second and third shells (known as the l and the m shells respectively). There are 18 each in the next two shells (known as the N and the o shells) and 32 in the next full p shell.<br />
<br />
=Atomic Number=<br />
Each of the chemical elements is made up of like atoms, also known as the atomic number. They all have the same number of protonss. Hydrogen (atmoic No. 1), has one proton and one planetary electron. The heaviest naturally occurring atom, has 92 protons and 92 electrons.<br><br />
Element 112 was discovered on 9th February 1996 in Darmstadt, Germany. The identified isotope currently is the heaviest atom ever produced by man and has an atomic mass of 277, that is, 277 times heavier than hydrogen. <br><br />
Except for hydrogen, all the other nuclei of atoms contain neutrons, varying from 2 in the case of helium to 146 in the uranium atom. The '''atomic weight''' of an element is the weight of the protons and neutrons, which form the nucleus of the atom. If an atom gains or loses one electron, it ceases to be electrically neutral and becomes what is known as an ion. the gaining of electrons, produces a negatively charged ion, known as an anion. Loss of electrons results in a positively charged ion referrred to as a cation.<br />
=Molecules=<br />
Atoms of elements can combine together to form tiny fractions of new substances. These are known as compounds. A molecule is defined as the smallest fraction of a substance, consisting of two or more elements, chemically combined together, which define a substance's composition and chemical properties.<br />
=Valency=<br />
The valency of an element is determined by the number of its atoms which will combine with, or replace, one atom of hydrogen. It can be observed that some elements will have different valencies in different compounds. For example, the compound FeO (ferrous oxide) is divalent and Fe2O3 (ferric oxide) is trivalent.<br />
=Isomorphism & Isomorphic Replacement=<br />
When two ions are brought together, there is a distance where a force of repulsion abruptly sets in and resists any closer approach. It is convenieent to consider the ions as "spheres" in contact, and the distance betweeen their centers is taken as the sum of the radiis of the two ions. An anion, such as an oxygen ion, have large ionic radii, where cations have radii that are much smaller.<br />
<br><br />
The common cations which enter the structure of crystals are often those with similar sized radii, and can replace each other within the structure without unduly straining the space lattice. This accounts for the phenomenon of isomorphism and isomorphic replacement.<br />
<br><br />
In the garnet and spinel groups, magnesia (MgO) and ferrous oxide (FeO) replace one another extensively. Likewise, alumina (Al2O3) and ferric oxide (Fe2O3) can easily replace each other within a crystal's lattice. When such a replacement takes place there can be a a significant variation in chemical composition, without much effecting the internal structure. This accounts for the fact that in certain gemstones of the same species, the specific gravity and refractive indices are not constant specimen to specimen. In some species like garnet, spinel, tourmaline, and beryl the values for refractive index and specific gravity can vary within wide parameters. This is an important factor to keep in mind when testing gemstones.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=The_Chemistry_of_Gemstones&diff=1588The Chemistry of Gemstones2006-03-05T23:04:14Z<p>Anatase: </p>
<hr />
<div>An '''element''' is a substance that can not be seperated into a simpler form of matter by ordinary means. An element may be a solid, liquid or a gas. <br><br />
Some common elements are carbon, gold, copper, iron, oxygen, silicon, etc.<br />
<br><br />
An '''atom''' is the smallest part of an element. It is the smallest, indivisible particle of a chemical element. Each atom consists of negatively charged electrons and positively charged protons. There are a similar number of electrons and protons to produce an electrically neutral atom. An atom can not be subdivided by any chemical process.<br />
[[Image:atom.gif]]<br><br />
=Electronic Configuration of Atoms=<br />
Properties of an element, chemical compounds and the formation of crystals depends a great deal on the disposition of electrons and their interaction. The electrons circle the nucleas in all directions, like a cloud. The radius of the average of their movements, is defined as a shell or energy level. These shells will remain at a predictible level which is determined by quantum mechanics. Each shell contains only a given number of electrons. There is a maximum of 2 in the innermost shell (known as the k shell), and 8 each in the second and third shells (known as the l and the m shells respectively). There are 18 each in the next two shells (known as the N and the o shells) and 32 in the next full p shell.<br />
=Atomic Number=<br />
Each of the chemical elements is made up of like atoms, also known as the atomic number. They all have the same number of protonss. Hydrogen (atmoic No. 1), has one proton and one planetary electron. The heaviest naturally occurring atom, has 92 protons and 92 electrons.<br><br />
Element 112 was discovered on 9th February 1996 in Darmstadt, Germany. The identified isotope currently is the heaviest atom ever produced by man and has an atomic mass of 277, that is, 277 times heavier than hydrogen. <br><br />
Except for hydrogen, all the other nuclei of atoms contain neutrons, varying from 2 in the case of helium to 146 in the uranium atom. The '''atomic weight''' of an element is the weight of the protons and neutrons, which form the nucleus of the atom. If an atom gains or loses one electron, it ceases to be electrically neutral and becomes what is known as an ion. the gaining of electrons, produces a negatively charged ion, known as an anion. Loss of electrons results in a positively charged ion referrred to as a cation.<br />
=Molecules=<br />
Atoms of elements can combine together to form tiny fractions of new substances. These are known as compounds. A molecule is defined as the smallest fraction of a substance, consisting of two or more elements, chemically combined together, which define a substance's composition and chemical properties.<br />
=Valency=<br />
The valency of an element is determined by the number of its atoms which will combine with, or replace, one atom of hydrogen. It can be observed that some elements will have different valencies in different compounds. For example, the compound FeO (ferrous oxide) is divalent and Fe2O3 (ferric oxide) is trivalent.<br />
=Isomorphism & Isomorphic Replacement=<br />
When two ions are brought together, there is a distance where a force of repulsion abruptly sets in and resists any closer approach. It is convenieent to consider the ions as "spheres" in contact, and the distance betweeen their centers is taken as the sum of the radiis of the two ions. An anion, such as an oxygen ion, have large ionic radii, where cations have radii that are much smaller.<br />
<br><br />
The common cations which enter the structure of crystals are often those with similar sized radii, and can replace each other within the structure without unduly straining the space lattice. This accounts for the phenomenon of isomorphism and isomorphic replacement.<br />
<br><br />
In the garnet and spinel groups, magnesia (MgO) and ferrous oxide (FeO) replace one another extensively. Likewise, alumina (Al2O3) and ferric oxide (Fe2O3) can easily replace each other within a crystal's lattice. When such a replacement takes place there can be a a significant variation in chemical composition, without much effecting the internal structure. This accounts for the fact that in certain gemstones of the same species, the specific gravity and refractive indices are not constant specimen to specimen. In some species like garnet, spinel, tourmaline, and beryl the values for refractive index and specific gravity can vary within wide parameters. This is an important factor to keep in mind when testing gemstones.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=The_Chemistry_of_Gemstones&diff=1587The Chemistry of Gemstones2006-03-05T23:02:25Z<p>Anatase: </p>
<hr />
<div>An '''element''' is a substance that can not be seperated into a simpler form of matter by ordinary means. An element may be a solid, liquid or a gas. <br><br />
Some common elements are carbon, gold, copper, iron, oxygen, silicon, etc.<br />
<br><br />
An '''atom'''is the smallest part of an element. It is the smallest, indivisible particle of a chemical element. Each atom consists of negatively charged electrons and positively charged protons. There are a similar number of electrons and protons to produce an electrically neutral atom. An atom can not be subdivided by any chemical process.<br />
[[Image:atom.gif]]<br><br />
=Electronic Configuration of Atoms=<br />
Properties of an element, chemical compounds and the formation of crystals depends a great deal on the disposition of electrons and their interaction. The electrons circle the nucleas in all directions, like a cloud. The radius of the average of their movements, is defined as a shell or energy level. These shells will remain at a predictible level which is determined by quantum mechanics. Each shell contains only a given number of electrons. There is a maximum of 2 in the innermost shell (known as the k shell), and 8 each in the second and third shells (known as the l and the m shells respectively). There are 18 each in the next two shells (known as the N and the o shells) and 32 in the next full p shell.<br />
=Atomic Number=<br />
Each of the chemical elements is made up of like atoms, also known as the atomic number. They all have the same number of protonss. Hydrogen (atmoic No. 1), has one proton and one planetary electron. The heaviest naturally occurring atom, has 92 protons and 92 electrons.<br><br />
Element 112 was discovered on 9th February 1996 in Darmstadt, Germany. The identified isotope currently is the heaviest atom ever produced by man and has an atomic mass of 277, that is, 277 times heavier than hydrogen. <br><br />
Except for hydrogen, all the other nuclei of atoms contain neutrons, varying from 2 in the case of helium to 146 in the uranium atom. The '''atomic weight''' of an element is the weight of the protons and neutrons, which form the nucleus of the atom. If an atom gains or loses one electron, it ceases to be electrically neutral and becomes what is known as an ion. the gaining of electrons, produces a negatively charged ion, known as an anion. Loss of electrons results in a positively charged ion referrred to as a cation.<br />
=Molecules=<br />
Atoms of elements can combine together to form tiny fractions of new substances. These are known as compounds. A molecule is defined as the smallest fraction of a substance, consisting of two or more elements, chemically combined together, which define a substance's composition and chemical properties.<br />
=Valency=<br />
The valency of an element is determined by the number of its atoms which will combine with, or replace, one atom of hydrogen. It can be observed that some elements will have different valencies in different compounds. For example, the compound FeO (ferrous oxide) is divalent and Fe2O3 (ferric oxide) is trivalent.<br />
=Isomorphism & Isomorphic Replacement=<br />
When two ions are brought together, there is a distance where a force of repulsion abruptly sets in and resists any closer approach. It is convenieent to consider the ions as "spheres" in contact, and the distance betweeen their centers is taken as the sum of the radiis of the two ions. An anion, such as an oxygen ion, have large ionic radii, where cations have radii that are much smaller.<br />
<br><br />
The common cations which enter the structure of crystals are often those with similar sized radii, and can replace each other within the structure without unduly straining the space lattice. This accounts for the phenomenon of isomorphism and isomorphic replacement.<br />
<br><br />
In the garnet and spinel groups, magnesia (MgO) and ferrous oxide (FeO) replace one another extensively. Likewise, alumina (Al2O3) and ferric oxide (Fe2O3) can easily replace each other within a crystal's lattice. When such a replacement takes place there can be a a significant variation in chemical composition, without much effecting the internal structure. This accounts for the fact that in certain gemstones of the same species, the specific gravity and refractive indices are not constant specimen to specimen. In some species like garnet, spinel, tourmaline, and beryl the values for refractive index and specific gravity can vary within wide parameters. This is an important factor to keep in mind when testing gemstones.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=The_Chemistry_of_Gemstones&diff=1586The Chemistry of Gemstones2006-03-05T22:41:32Z<p>Anatase: </p>
<hr />
<div>An '''element''' is a substance that can not be seperated into a simpler form of matter by ordinary means. An element may be a solid, liquid or a gas. <br><br />
Some common elements are carbon, gold, copper, iron, oxygen, silicon, etc.<br />
<br><br />
An '''atom'''is the smallest part of an element. It is the smallest, indivisible particle of a chemical element. Each atom consists of negatively charged electrons and positively charged protons. There are a similar number of electrons and protons to produce an electrically neutral atom. An atom can not be subdivided by any chemical process.<br />
[[Image:atom.gif]]<br><br />
=Electronic Configuration of Atoms=<br />
Properties of an element, chemical compounds and the formation of crystals depends a great deal on the disposition of electrons and their interaction. The electrons circle the nucleas in all directions, like a cloud. The radius of the average of their movements, is defined as a shell or energy level. These shells will remain at a predictible level which is determined by quantum mechanics. Each shell contains only a given number of electrons. There is a maximum of 2 in the innermost shell (known as the k shell), and 8 each in the second and third shells (known as the l and the m shells respectively). There are 18 each in the next two shells (known as the N and the o shells) and 32 in the next full p shell.<br />
=Atomic Number=<br />
Each of the chemical elements is made up of like atoms, also known as the atomic number. They all have the same number of protonss. Hydrogen (atmoic No. 1), has one proton and one planetary electron. The heaviest naturally occurring atom, has 92 protons and 92 electrons.<br><br />
Element 112 was discovered on 9th February 1996 in Darmstadt, Germany. The identified isotope currently is the heaviest atom ever produced by man and has an atomic mass of 277, that is, 277 times heavier than hydrogen. <br><br />
Except for hydrogen, all the other nuclei of atoms contain neutrons, varying from 2 in the case of helium to 146 in the uranium atom. The '''atomic weight''' of an element is the weight of the protons and neutrons, which form the nucleus of the atom. If an atom gains or loses one electron, it ceases to be electrically neutral and becomes what is known as an ion. the gaining of electrons, produces a negatively charged ion, known as an anion. Loss of electrons results in a positively charged ion referrred to as a cation.<br />
=Molecules=<br />
Atoms of elements can combine together to form tiny fractions of new substances. These are known as compounds. A molecule is defined as the smallest fraction of a substance, consisting of two or more elements, chemically combined together, which define a substance's composition and chemical properties.<br />
=Valency=<br />
The valency of an element is determined by the number of its atoms which will combine with, or replace, one atom of hydrogen. It can be observed that some elements will have different valencies in different compounds. For example, the compound FeO (ferrous oxide) is divalent and Fe2O3 (ferric oxide) is trivalent.<br />
=Isomorphism & Isomorphic Replacement=</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Table_Of_Contents&diff=1585Table Of Contents2006-03-05T22:40:51Z<p>Anatase: </p>
<hr />
<div>This should hold a logical and an easy to navigate content table.<br />
Doesn't matter if the articles are written yet or not.<br />
<br />
Something like:<br />
<br />
#'''Content'''<br />
##[[Introduction to Gemology]]<br />
###[[An Historical Look at our Obsession with Gems]]<br />
##[[Origins of minerals]]<br />
###[[Origins_of_minerals#Igneous_.28Magmatic.29_rocks|Igneous rocks]]<br />
###[[Origins_of_minerals#Sedimentary_rocks|Sedimentary rocks]]<br />
###[[Origins_of_minerals#Metamorphic_rocks|Metamorphic rocks]]<br />
##[[The Chemistry of Gemstones]]<br />
##[[Chemical Classification of Gems & Gemstones]]<br />
###[[Class I: Pure Elements]]<br />
###[[Class II: Sulphides]]<br />
###[[Class III: Halides]]<br />
###[[Class IV: Oxides]]<br />
###[[Class V a:Carbonates]]<br />
###[[Class V b:Borates]]<br />
###[[Class VI a:Tungstates]]<br />
###[[Class VI b:Sulphates]]<br />
###[[Class VII: Phosphates]]<br />
###[[Class VIII: Silicates]]<br />
###[[Non-Crystalline & Organic Gems]]<br />
##[[Crystal Systems & Forms]]<br />
###[[Crystals & Their Structure]]<br />
####[[Cubic Crystal System]]<br />
####[[Hexagonal Crystal System]]<br />
####[[Tetragonal Crystal System]]<br />
####[[Trigonal Crystal System]]<br />
####[[Rhombic Crystal System]]<br />
####[[Monoclinic Crystal System]]<br />
####[[Triclinic Crystal System]]<br />
###[[Symmetry]]<br />
####[[Axis of Symmetry]]<br />
####[[Plane of Symmetry]]<br />
####[[Center of Symmetry]]<br />
###[[Twin Crystals]]<br />
###[[Naming minerals]]<br />
##[[Cleavage]]<br />
###[[Cubic Cleavage]]<br />
###[[Octahedral Cleavage]]<br />
###[[Rhombohedral Cleavage]]<br />
###[[Basal Cleavage]]<br />
###[[Prismatic Cleavage]]<br />
###[[Dodecahedral Cleavage]]<br />
##[[Optical properties of gemstones]]<br />
###[[Nature of light]]<br />
####[[Nature_of_light#The_electromagnetic_wave_theory |The electromagnetic wave theory]]<br />
####[[Nature_of_light#The_quantum_theory |The quantum theory]]<br />
####[[Nature_of_light#The_electromagnetic_spectrum |The electromagnetic spectrum]]<br />
###[[Reflection effects]]<br />
####[[Lustre]]<br />
####[[Sheen]]<br />
#####[[Sheen#Chatoyancy | Chatoyancy]]<br />
#####[[Sheen#Asterism | Asterism]]<br />
#####[[Sheen#Iridescence | Iridescence]]<br />
####[[Brilliance]]<br />
###[[Polarization]]<br />
###[[Pleochroism]]<br />
###[[Color]]<br />
###[[Refraction]]<br />
###[[Dispersion]]<br />
###[[Diffraction]]<br />
<br />
<br />
[[category:gemology]]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=File:Atom.gif&diff=1583File:Atom.gif2006-03-05T21:42:41Z<p>Anatase: </p>
<hr />
<div></div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Sheen&diff=1582Sheen2006-03-05T18:45:09Z<p>Anatase: /* Iridescence */</p>
<hr />
<div>Sheen is the effect caused by reflection of light from below the surface of the gemstone (lustre is on the surface).<br />
<br />
There are several terms associated with sheen (listed below) and the causes can range from inclusions, internal<br />
structures and interference.<br />
<br />
==Chatoyancy==<br />
<br />
This type of sheen occurs on gemstones with parallel orientated inclusions, like fibers, needles and hollow tubes.<br />
The effect of the reflection on these parallel arranged needles, fibres or hollow tubes is a light streak which runs at<br />
a 90° angle over the inclusions.<br />
<br />
In order for this effect to be seen, the gemstone needs to be cut en-cabochon.<br><br />
Naming these types of gemstones is generally done with the suffix ''Cat's-Eye'', as in ''Alexandrite Cat's-Eye''.<br><br />
<br />
[[Image:crysoberyl.jpg]]<br><br />
<br />
Famous examples of this type of sheen are Chrysoberyl Cat's-Eye (or "Cymophane") and Tiger's-Eye (Quartz with asbestos fibres).<br><br />
[[Image:Tigerye.jpg]]<br><br />
Others gemstones that may show chatoyancy are:<br />
* Quartz<br />
* Tourmaline<br />
* Apatite<br />
* Beryl<br />
* Alexandrite<br />
* Emerald<br />
<br />
==Asterism==<br />
<br />
Asterism is, like chatoyancy, caused by reflection on inclusions. However the inclusions are aranged in different<br />
directions causing several lightstreaks on the surface of the en-cabochon stone.<br />
<br />
There can be 4-pointed, 6-pointed and 12-pointed stars.<br><br />
[[Image:Stars.jpg]]<br><br />
In general the inclusions which cause the stars are orientated parallel to the crystal faces.<br><br />
In Corundum you may find (usually in Thai sapphire) a 12-pointed star due to inclusions (rutile and hematite) following<br />
both the 1st order and the 2nd order prism.<br />
<br />
This type of asterism (due to reflected light) is named ''epiasterim''.<br><br />
''Diasterism'' is asterism caused by transmitted light (from behind the stone) and can be seen in some Rose Quartz and Almandine Garnet.<br />
<br />
Garnet may produce 4-pointed stars which intersect at 90°, whilst in Diopside the 4-pointed stars intersect at 73°.<br><br />
Corundum usually forms 6-pointed stars (mostly due to rutile or hematite needles).<br />
<br />
Synthetic corundum may also show asterism. Usually the stars are much better defined than their natural counterparts.<br />
<br />
Emerald has been reported to show a 6-pointed star.<br />
<br />
Some stones, especially corundum, have orientated inclusions but in insufficient quantities to show a star.<br><br />
These stones are generally facetted and occasionally you may see light reflected from small groups of such inclusions. This is termed ''Silk''.<br />
<br />
We describe stones which show asterism with the prefix ''Star'' as in ''Star-Emerald''.<br />
<br />
Some gemstones that may show asterism:<br />
* Ruby (6-pointed)<br />
* Sapphire (6-pointed, rarely 12-pointed)<br />
* Rose Quartz (6-pointed)<br />
* Spinel (4 or 6-pointed)<br />
* Garnet (4 or 6-pointed)<br />
* Diopside (4-pointed)<br />
<br />
==Iridescence==<br />
<br />
Iridescence is the play of color, or a series of colors, produced by [[interference]] or [[diffraction]] (or both), either when light is reflected from thin films, twinning planes or from the unique structure of precious opal.<br />
<br />
There are several types of iridescence that have their own particular causes:<br />
* Labradorescence<br />
* Adularescence (or Schiller)<br />
* Aventurescence<br />
* Opalescence <br><br />
<br />
<br />
===Labradorescence===</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Sheen&diff=1581Sheen2006-03-05T18:39:14Z<p>Anatase: /* Iridescence */</p>
<hr />
<div>Sheen is the effect caused by reflection of light from below the surface of the gemstone (lustre is on the surface).<br />
<br />
There are several terms associated with sheen (listed below) and the causes can range from inclusions, internal<br />
structures and interference.<br />
<br />
==Chatoyancy==<br />
<br />
This type of sheen occurs on gemstones with parallel orientated inclusions, like fibers, needles and hollow tubes.<br />
The effect of the reflection on these parallel arranged needles, fibres or hollow tubes is a light streak which runs at<br />
a 90° angle over the inclusions.<br />
<br />
In order for this effect to be seen, the gemstone needs to be cut en-cabochon.<br><br />
Naming these types of gemstones is generally done with the suffix ''Cat's-Eye'', as in ''Alexandrite Cat's-Eye''.<br><br />
<br />
[[Image:crysoberyl.jpg]]<br><br />
<br />
Famous examples of this type of sheen are Chrysoberyl Cat's-Eye (or "Cymophane") and Tiger's-Eye (Quartz with asbestos fibres).<br><br />
[[Image:Tigerye.jpg]]<br><br />
Others gemstones that may show chatoyancy are:<br />
* Quartz<br />
* Tourmaline<br />
* Apatite<br />
* Beryl<br />
* Alexandrite<br />
* Emerald<br />
<br />
==Asterism==<br />
<br />
Asterism is, like chatoyancy, caused by reflection on inclusions. However the inclusions are aranged in different<br />
directions causing several lightstreaks on the surface of the en-cabochon stone.<br />
<br />
There can be 4-pointed, 6-pointed and 12-pointed stars.<br><br />
[[Image:Stars.jpg]]<br><br />
In general the inclusions which cause the stars are orientated parallel to the crystal faces.<br><br />
In Corundum you may find (usually in Thai sapphire) a 12-pointed star due to inclusions (rutile and hematite) following<br />
both the 1st order and the 2nd order prism.<br />
<br />
This type of asterism (due to reflected light) is named ''epiasterim''.<br><br />
''Diasterism'' is asterism caused by transmitted light (from behind the stone) and can be seen in some Rose Quartz and Almandine Garnet.<br />
<br />
Garnet may produce 4-pointed stars which intersect at 90°, whilst in Diopside the 4-pointed stars intersect at 73°.<br><br />
Corundum usually forms 6-pointed stars (mostly due to rutile or hematite needles).<br />
<br />
Synthetic corundum may also show asterism. Usually the stars are much better defined than their natural counterparts.<br />
<br />
Emerald has been reported to show a 6-pointed star.<br />
<br />
Some stones, especially corundum, have orientated inclusions but in insufficient quantities to show a star.<br><br />
These stones are generally facetted and occasionally you may see light reflected from small groups of such inclusions. This is termed ''Silk''.<br />
<br />
We describe stones which show asterism with the prefix ''Star'' as in ''Star-Emerald''.<br />
<br />
Some gemstones that may show asterism:<br />
* Ruby (6-pointed)<br />
* Sapphire (6-pointed, rarely 12-pointed)<br />
* Rose Quartz (6-pointed)<br />
* Spinel (4 or 6-pointed)<br />
* Garnet (4 or 6-pointed)<br />
* Diopside (4-pointed)<br />
<br />
==Iridescence==<br />
<br />
Iridescence is the play of color, or a series of colors, produced by [[interference]] or [[diffraction]] (or both), either when light is reflected from thin films, twinning planes or from the unique structure of precious opal.<br />
<br />
There are several types of iridescence that have their own particular causes:<br />
* Labradorescence<br />
* Adularescence (or Schiller)<br />
* Aventurescence<br />
* Opalescence <br><br />
[[Image:Phen.jpg]]<br />
<br />
===Labradorescence===</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Sheen&diff=1579Sheen2006-03-05T17:56:41Z<p>Anatase: /* Asterism */</p>
<hr />
<div>Sheen is the effect caused by reflection of light from below the surface of the gemstone (lustre is on the surface).<br />
<br />
There are several terms associated with sheen (listed below) and the causes can range from inclusions, internal<br />
structures and interference.<br />
<br />
==Chatoyancy==<br />
<br />
This type of sheen occurs on gemstones with parallel orientated inclusions, like fibers, needles and hollow tubes.<br />
The effect of the reflection on these parallel arranged needles, fibres or hollow tubes is a light streak which runs at<br />
a 90° angle over the inclusions.<br />
<br />
In order for this effect to be seen, the gemstone needs to be cut en-cabochon.<br><br />
Naming these types of gemstones is generally done with the suffix ''Cat's-Eye'', as in ''Alexandrite Cat's-Eye''.<br><br />
<br />
[[Image:crysoberyl.jpg]]<br><br />
<br />
Famous examples of this type of sheen are Chrysoberyl Cat's-Eye (or "Cymophane") and Tiger's-Eye (Quartz with asbestos fibres).<br><br />
[[Image:Tigerye.jpg]]<br><br />
Others gemstones that may show chatoyancy are:<br />
* Quartz<br />
* Tourmaline<br />
* Apatite<br />
* Beryl<br />
* Alexandrite<br />
* Emerald<br />
<br />
==Asterism==<br />
<br />
Asterism is, like chatoyancy, caused by reflection on inclusions. However the inclusions are aranged in different<br />
directions causing several lightstreaks on the surface of the en-cabochon stone.<br />
<br />
There can be 4-pointed, 6-pointed and 12-pointed stars.<br><br />
[[Image:Stars.jpg]]<br><br />
In general the inclusions which cause the stars are orientated parallel to the crystal faces.<br><br />
In Corundum you may find (usually in Thai sapphire) a 12-pointed star due to inclusions (rutile and hematite) following<br />
both the 1st order and the 2nd order prism.<br />
<br />
This type of asterism (due to reflected light) is named ''epiasterim''.<br><br />
''Diasterism'' is asterism caused by transmitted light (from behind the stone) and can be seen in some Rose Quartz and Almandine Garnet.<br />
<br />
Garnet may produce 4-pointed stars which intersect at 90°, whilst in Diopside the 4-pointed stars intersect at 73°.<br><br />
Corundum usually forms 6-pointed stars (mostly due to rutile or hematite needles).<br />
<br />
Synthetic corundum may also show asterism. Usually the stars are much better defined than their natural counterparts.<br />
<br />
Emerald has been reported to show a 6-pointed star.<br />
<br />
Some stones, especially corundum, have orientated inclusions but in insufficient quantities to show a star.<br><br />
These stones are generally facetted and occasionally you may see light reflected from small groups of such inclusions. This is termed ''Silk''.<br />
<br />
We describe stones which show asterism with the prefix ''Star'' as in ''Star-Emerald''.<br />
<br />
Some gemstones that may show asterism:<br />
* Ruby (6-pointed)<br />
* Sapphire (6-pointed, rarely 12-pointed)<br />
* Rose Quartz (6-pointed)<br />
* Spinel (4 or 6-pointed)<br />
* Garnet (4 or 6-pointed)<br />
* Diopside (4-pointed)<br />
<br />
==Iridescence==<br />
<br />
Iridescence is the play of color, or a series of colors, produced by [[interference]] or [[diffraction]] (or both), either when light is reflected from thin films, twinning planes or from the unique structure of precious opal.<br />
<br />
There are several types of iridescence that have their own particular causes:<br />
* Labradorescence<br />
* Adularescence (or Schiller)<br />
* Aventurescence<br />
* Opalescence<br />
<br />
===Labradorescence===</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=File:Stars.jpg&diff=1577File:Stars.jpg2006-03-05T17:53:13Z<p>Anatase: </p>
<hr />
<div></div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Sheen&diff=1576Sheen2006-03-05T17:39:16Z<p>Anatase: /* Chatoyancy */</p>
<hr />
<div>Sheen is the effect caused by reflection of light from below the surface of the gemstone (lustre is on the surface).<br />
<br />
There are several terms associated with sheen (listed below) and the causes can range from inclusions, internal<br />
structures and interference.<br />
<br />
==Chatoyancy==<br />
<br />
This type of sheen occurs on gemstones with parallel orientated inclusions, like fibers, needles and hollow tubes.<br />
The effect of the reflection on these parallel arranged needles, fibres or hollow tubes is a light streak which runs at<br />
a 90° angle over the inclusions.<br />
<br />
In order for this effect to be seen, the gemstone needs to be cut en-cabochon.<br><br />
Naming these types of gemstones is generally done with the suffix ''Cat's-Eye'', as in ''Alexandrite Cat's-Eye''.<br><br />
<br />
[[Image:crysoberyl.jpg]]<br><br />
<br />
Famous examples of this type of sheen are Chrysoberyl Cat's-Eye (or "Cymophane") and Tiger's-Eye (Quartz with asbestos fibres).<br><br />
[[Image:Tigerye.jpg]]<br><br />
Others gemstones that may show chatoyancy are:<br />
* Quartz<br />
* Tourmaline<br />
* Apatite<br />
* Beryl<br />
* Alexandrite<br />
* Emerald<br />
<br />
==Asterism==<br />
<br />
Asterism is, like chatoyancy, caused by reflection on inclusions. However the inclusions are aranged in different<br />
directions causing several lightstreaks on the surface of the en-cabochon stone.<br />
<br />
There can be 4-pointed, 6-pointed and 12-pointed stars.<br />
<br />
In general the inclusions which cause the stars are orientated parallel to the crystal faces.<br><br />
In Corundum you may find (usually in Thai sapphire) a 12-pointed star due to inclusions (rutile and hematite) following<br />
both the 1st order and the 2nd order prism.<br />
<br />
This type of asterism (due to reflected light) is named ''epiasterim''.<br><br />
''Diasterism'' is asterism caused by transmitted light (from behind the stone) and can be seen in some Rose Quartz and Almandine Garnet.<br />
<br />
Garnet may produce 4-pointed stars which intersect at 90°, whilst in Diopside the 4-pointed stars intersect at 73°.<br><br />
Corundum usually forms 6-pointed stars (mostly due to rutile or hematite needles).<br />
<br />
Synthetic corundum may also show asterism. Usually the stars are much better defined than their natural counterparts.<br />
<br />
Emerald has been reported to show a 6-pointed star.<br />
<br />
Some stones, especially corundum, have orientated inclusions but in insufficient quantities to show a star.<br><br />
These stones are generally facetted and occasionally you may see light reflected from small groups of such inclusions. This is termed ''Silk''.<br />
<br />
We describe stones which show asterism with the prefix ''Star'' as in ''Star-Emerald''.<br />
<br />
Some gemstones that may show asterism:<br />
* Ruby (6-pointed)<br />
* Sapphire (6-pointed, rarely 12-pointed)<br />
* Rose Quartz (6-pointed)<br />
* Spinel (4 or 6-pointed)<br />
* Garnet (4 or 6-pointed)<br />
* Diopside (4-pointed)<br />
<br />
==Iridescence==<br />
<br />
Iridescence is the play of color, or a series of colors, produced by [[interference]] or [[diffraction]] (or both), either when light is reflected from thin films, twinning planes or from the unique structure of precious opal.<br />
<br />
There are several types of iridescence that have their own particular causes:<br />
* Labradorescence<br />
* Adularescence (or Schiller)<br />
* Aventurescence<br />
* Opalescence<br />
<br />
===Labradorescence===</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=File:Tigerye.jpg&diff=1575File:Tigerye.jpg2006-03-05T17:36:05Z<p>Anatase: </p>
<hr />
<div></div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Sheen&diff=1572Sheen2006-03-05T17:23:23Z<p>Anatase: /* Chatoyancy */</p>
<hr />
<div>Sheen is the effect caused by reflection of light from below the surface of the gemstone (lustre is on the surface).<br />
<br />
There are several terms associated with sheen (listed below) and the causes can range from inclusions, internal<br />
structures and interference.<br />
<br />
==Chatoyancy==<br />
<br />
This type of sheen occurs on gemstones with parallel orientated inclusions, like fibers, needles and hollow tubes.<br />
The effect of the reflection on these parallel arranged needles, fibres or hollow tubes is a light streak which runs at<br />
a 90° angle over the inclusions.<br />
<br />
In order for this effect to be seen, the gemstone needs to be cut en-cabochon.<br><br />
Naming these types of gemstones is generally done with the suffix ''Cat's-Eye'', as in ''Alexandrite Cat's-Eye''.<br><br />
[[Image:crysoberyl.jpg]]<br><br />
<br />
Famous examples of this type of sheen are Chrysoberyl Cat's-Eye (or "Cymophane") and Tiger's-Eye (Quartz with asbestos fibres).<br />
<br />
Others gemstones that may show chatoyancy are:<br />
* Quartz<br />
* Tourmaline<br />
* Apatite<br />
* Beryl<br />
* Alexandrite<br />
* Emerald<br />
<br />
==Asterism==<br />
<br />
Asterism is, like chatoyancy, caused by reflection on inclusions. However the inclusions are aranged in different<br />
directions causing several lightstreaks on the surface of the en-cabochon stone.<br />
<br />
There can be 4-pointed, 6-pointed and 12-pointed stars.<br />
<br />
In general the inclusions which cause the stars are orientated parallel to the crystal faces.<br><br />
In Corundum you may find (usually in Thai sapphire) a 12-pointed star due to inclusions (rutile and hematite) following<br />
both the 1st order and the 2nd order prism.<br />
<br />
This type of asterism (due to reflected light) is named ''epiasterim''.<br><br />
''Diasterism'' is asterism caused by transmitted light (from behind the stone) and can be seen in some Rose Quartz and Almandine Garnet.<br />
<br />
Garnet may produce 4-pointed stars which intersect at 90°, whilst in Diopside the 4-pointed stars intersect at 73°.<br><br />
Corundum usually forms 6-pointed stars (mostly due to rutile or hematite needles).<br />
<br />
Synthetic corundum may also show asterism. Usually the stars are much better defined than their natural counterparts.<br />
<br />
Emerald has been reported to show a 6-pointed star.<br />
<br />
Some stones, especially corundum, have orientated inclusions but in insufficient quantities to show a star.<br><br />
These stones are generally facetted and occasionally you may see light reflected from small groups of such inclusions. This is termed ''Silk''.<br />
<br />
We describe stones which show asterism with the prefix ''Star'' as in ''Star-Emerald''.<br />
<br />
Some gemstones that may show asterism:<br />
* Ruby (6-pointed)<br />
* Sapphire (6-pointed, rarely 12-pointed)<br />
* Rose Quartz (6-pointed)<br />
* Spinel (4 or 6-pointed)<br />
* Garnet (4 or 6-pointed)<br />
* Diopside (4-pointed)<br />
<br />
==Iridescence==<br />
<br />
Iridescence is the play of color, or a series of colors, produced by [[interference]] or [[diffraction]] (or both), either when light is reflected from thin films, twinning planes or from the unique structure of precious opal.<br />
<br />
There are several types of iridescence that have their own particular causes:<br />
* Labradorescence<br />
* Adularescence (or Schiller)<br />
* Aventurescence<br />
* Opalescence<br />
<br />
===Labradorescence===</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=File:Crysoberyl.jpg&diff=1571File:Crysoberyl.jpg2006-03-05T17:19:17Z<p>Anatase: </p>
<hr />
<div></div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Introduction_to_Gemology&diff=1563Introduction to Gemology2006-03-05T16:09:09Z<p>Anatase: /* DGemG */</p>
<hr />
<div>==General information on Gemology==<br />
<br />
===What is Gemology===<br />
<br />
'''Gemology''' is the science and study of gemstones, which often involves the study of mineralogical fundamentals such as formations, genesis, localities, physical properties and identification of gemstones. It includes the basic knowledge of structural, crystallographic, chemical and physical characteristics and properties of gems. It also involves the way in which gemstones are fashioned.<br />
<br />
''Special Gemology'' deals with categories and varieties of gemstones, synthetic stones and imitations. Conventionally, the organic substances such as amber, pearls, coral and the non-minerals are also included in this subject of special gemology.<br />
<br />
''Practical Gemology'' refers to the application of the knowledge of characteristics and properties of gemstones in identification or separation of synthetics and imitations. Diamond grading is included in practical gemology.<br />
<br />
===What is a Gemologist===<br />
<br />
A gemologist is someone who studies gemstones. Being recognized as a gemologist usually involves having credentials from one of the Institutes for Gem(m)ological Studies discussed below (see '''Becoming a Gemologist''').<br />
<br />
===What are gemstones===<br />
<br />
Gemstones are usually [[mineral]]s but sometimes [[inorganic]] substances.<br />
What separates them from minerals in general is that they are used in jewelry.<br><br />
That is a very thin line of separation, but usually we take 4 factors into account:<br />
<br />
* [[Durability]]<br />
* [[Rarity]]<br />
* [[Beauty]]<br />
* [[Price]]<br />
<br />
And of course the 5th factor:<br />
<br />
* [[Fashion]]<br />
<br />
All the factors above are very subjective, for instance [[Amber]] has very poor durabilty, isn't very rare and in<br />
general is not highly priced. Yet it is considered to be a gem due to its beauty.<br />
On the counterpart, most [[Sapphire]] has good durability but can be very unattractive and cheap. Only a small portion of<br />
all Sapphires mined have good color/beauty.<br />
<br />
==Becoming a Gemologist==<br />
<br />
Becoming a gemologist in general means hard work and commitment. A wise teacher once said "You are only permitted to read books related to our trade and a religious book of your choice from now on . . . for the rest of your life".<br />
<br />
===Education===<br />
<br />
====Gem-A====<br />
<br />
Better known as The Gemmological Association and Gem Testing Laboratory of Great-Britain,<br> <br />
this school is London based with departments worldwide. It offers distance tutoring as well as through teaching centers.<br><br />
The primary focus is on indepth theory and the exams are the hardest to take in the industry. A fellowship of Gem-A means esteem. <br />
<br />
Costs:<br />
<br />
Foundation correspondence course GBP 993.00<br><br />
Diploma correspondence course GBP 1356.00 (on completion is granted the FGA title).<br />
<br />
Gem Diamond diploma course GBP 1584.00 (on completion is granted the DGA title).<br />
<br />
Website http://gem-a.info/<br />
<br />
====GIA====<br />
<br />
The Gemological Institute of America is the most prestigious and respected institute for gemology within the United States. Its main location is in Carlsbad, California, with facilities in New York and Los Angeles. Correspondence courses are available and encouraged. <br />
It was established in 1931, and currently the GIA is the world’s largest and one of the most respected nonprofit institutes of gemological research and learning internationally.<br />
It employs nearly 900, including scientists, diamond graders, and educators.<br />
<br />
Costs:<br />
<br />
On campus (CB/NY/LA): 6 month continuous program (780 hours) $13,995<br />
<br />
Distance Education: GEM130, GEM230, GEM230L, GEM120, GEM220,GEM220L, GEM240, GEM240L (Maximum completion time: 63 months) $6,975 ($7,395 International)<br />
<br />
What you earn: Graduate Gemologist Diploma, Graduate Diamonds Diploma, Graduate Colored Stones Diploma<br><br />
Website: http://www.gia.edu<br />
<br />
====AIGS====<br />
Thailand is in the heart of Southeast Asia 's gem and jewelry production and trading area. It presents you with an extraordinary opportunity to learn gemology in theory and practice while experiencing the gem business in a three dimensional way. <br />
<br />
The A.G. program, which leads to the A.G. (Accredited Gemologist) Diploma, includes the four core courses:<br> <br />
:E102: Gem Identification<br><br />
:E103: Diamond Grading and Pricing<br><br />
:E201: Colored Stone Grading and Pricing<br><br />
:E301: Synthetic and Treated Gem Identification. <br />
<br />
These 4 courses can be studied in any order, in one or several study periods at AIGS. It is recommended that “Gem Identification” be studied before “Synthethics and Treated Gems”. <br />
<br />
Students enrolling in the entire A.G. program are entitled to a 15% discount off the total tuition fee. Courses must be taken within one year of the first date of payment. Beyond the one year period, students will be subjected to any tuition increases that may have occurred. (Example: Old fee = 20,000 Baht, New fee in effect since date of enrollment = 22,000 Baht, Additional amount to be paid = 2,000 Baht.)<br />
<br />
Living expenses and general overhead are amazingly low compared to countries such as USA, Japan and most of Europe. Students studying at the AIGS can live with a US$600 to US$1000 budget per month including lodging near the school, weekend field trips, restaurants and entertainment. Of course, you can spend much more if you want to, but this amount yields a comfortable lifestyle!<br><br />
Website: http://www.aigsthailand.com/<br />
<br />
====DGemG====<br />
The Deutsche Gemmologische Gesellschaft (The Educational Training Center of the German Gemmological Association) is located in Idar-Oberstein, Germany. Idar-Oberstin is an international colored stone gem capital, where gem cutting has been traditionally mastered for centuries. It is currently bustling with local gem artists and studios. It has, perhaps, the highest per capita population of gem cutters in the world! The German Gemmological Association was founded in 1932.<br />
Its laboratories have modern state of the art equipment, and one of the most extensive colored and exotic gemstone collections available.<br />
<br />
Costs:<br />
<br />
Euro 5,800.00 <br><br />
<br />
Website:http://www.dgemg.de/gemmologen_eng/index.php?seite=home<br />
<br />
====FGAA====<br />
<br />
The Gemmological Association of Australia (GAA), founded in 1945, is Australia’s historic trade-accepted non-profit educational authority for gemmology. <br><br />
They offer gemmological courses in 6 state divisions.<br />
<br />
Costs: contact one of the six state divisions for pricing.<br />
<br />
Website: [http://www.gem.org.au www.gem.org.au]<br />
<br />
====CGA====<br />
<br />
The Canadian Gemmological Association, based in Toronto Canada, is a Canada-wide professional organization which has set the standard for excellence in the practice of gemmology. It was founded in 1958 by Dean S.M. Field, and has since provided training in gemmology to persons dealing with gemstones in the jewellery industry and to hobbyists for better appreciation and possible new career opportunities within gemmology.<br />
<br />
They offer a years correspondence course as well classes on location.<br />
<br />
Costs:<br />
<br />
The two year correspondence course, leading to a Diploma in Gemmology and a Fellowship (FCGmA) in the Canadian Gemmological Association, is offered for CAD 2,020.00<br />
<br />
Webite [http://www.canadiangemmological.com/ canadagemmological.com]<br />
<br />
===Post Graduate===<br />
<br />
After gaining your gemological diploma, the real fun starts. You will know the basics and more importantly you will know how to read the many articles published in various [[periodicals]].<br><br />
If you keep up to date and involved, you will be a good gemologist one day.<br />
<br />
====Career Opportunities====<br />
<br />
As with any profession, it is all up to you what you will become and what your salary will be.<br />
<br />
Think of a gemological diploma as if you have finished your first year in college and the payrate according to that when you start out.<br><br />
You will be qualified to find jobs in gemological laboratories worldwide, be the key figure in the local jewelry store, manager of a tellsell company, start your own gemtrading business, become an appraiser, shoveling municipal gardens etc.<br><br />
Anything you set your mind to.<br />
<br />
Payrate is according to experience, but a starting wage of USD 20,000.00 sounds fair (depending on locality/age/experience ofcourse).<br><br />
Best advice is to start networking from the start and to seek a new employer every few years so you can gain as much know-how as you can.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Introduction_to_Gemology&diff=1562Introduction to Gemology2006-03-05T16:08:00Z<p>Anatase: /* AIGS */</p>
<hr />
<div>==General information on Gemology==<br />
<br />
===What is Gemology===<br />
<br />
'''Gemology''' is the science and study of gemstones, which often involves the study of mineralogical fundamentals such as formations, genesis, localities, physical properties and identification of gemstones. It includes the basic knowledge of structural, crystallographic, chemical and physical characteristics and properties of gems. It also involves the way in which gemstones are fashioned.<br />
<br />
''Special Gemology'' deals with categories and varieties of gemstones, synthetic stones and imitations. Conventionally, the organic substances such as amber, pearls, coral and the non-minerals are also included in this subject of special gemology.<br />
<br />
''Practical Gemology'' refers to the application of the knowledge of characteristics and properties of gemstones in identification or separation of synthetics and imitations. Diamond grading is included in practical gemology.<br />
<br />
===What is a Gemologist===<br />
<br />
A gemologist is someone who studies gemstones. Being recognized as a gemologist usually involves having credentials from one of the Institutes for Gem(m)ological Studies discussed below (see '''Becoming a Gemologist''').<br />
<br />
===What are gemstones===<br />
<br />
Gemstones are usually [[mineral]]s but sometimes [[inorganic]] substances.<br />
What separates them from minerals in general is that they are used in jewelry.<br><br />
That is a very thin line of separation, but usually we take 4 factors into account:<br />
<br />
* [[Durability]]<br />
* [[Rarity]]<br />
* [[Beauty]]<br />
* [[Price]]<br />
<br />
And of course the 5th factor:<br />
<br />
* [[Fashion]]<br />
<br />
All the factors above are very subjective, for instance [[Amber]] has very poor durabilty, isn't very rare and in<br />
general is not highly priced. Yet it is considered to be a gem due to its beauty.<br />
On the counterpart, most [[Sapphire]] has good durability but can be very unattractive and cheap. Only a small portion of<br />
all Sapphires mined have good color/beauty.<br />
<br />
==Becoming a Gemologist==<br />
<br />
Becoming a gemologist in general means hard work and commitment. A wise teacher once said "You are only permitted to read books related to our trade and a religious book of your choice from now on . . . for the rest of your life".<br />
<br />
===Education===<br />
<br />
====Gem-A====<br />
<br />
Better known as The Gemmological Association and Gem Testing Laboratory of Great-Britain,<br> <br />
this school is London based with departments worldwide. It offers distance tutoring as well as through teaching centers.<br><br />
The primary focus is on indepth theory and the exams are the hardest to take in the industry. A fellowship of Gem-A means esteem. <br />
<br />
Costs:<br />
<br />
Foundation correspondence course GBP 993.00<br><br />
Diploma correspondence course GBP 1356.00 (on completion is granted the FGA title).<br />
<br />
Gem Diamond diploma course GBP 1584.00 (on completion is granted the DGA title).<br />
<br />
Website http://gem-a.info/<br />
<br />
====GIA====<br />
<br />
The Gemological Institute of America is the most prestigious and respected institute for gemology within the United States. Its main location is in Carlsbad, California, with facilities in New York and Los Angeles. Correspondence courses are available and encouraged. <br />
It was established in 1931, and currently the GIA is the world’s largest and one of the most respected nonprofit institutes of gemological research and learning internationally.<br />
It employs nearly 900, including scientists, diamond graders, and educators.<br />
<br />
Costs:<br />
<br />
On campus (CB/NY/LA): 6 month continuous program (780 hours) $13,995<br />
<br />
Distance Education: GEM130, GEM230, GEM230L, GEM120, GEM220,GEM220L, GEM240, GEM240L (Maximum completion time: 63 months) $6,975 ($7,395 International)<br />
<br />
What you earn: Graduate Gemologist Diploma, Graduate Diamonds Diploma, Graduate Colored Stones Diploma<br><br />
Website: http://www.gia.edu<br />
<br />
====AIGS====<br />
Thailand is in the heart of Southeast Asia 's gem and jewelry production and trading area. It presents you with an extraordinary opportunity to learn gemology in theory and practice while experiencing the gem business in a three dimensional way. <br />
<br />
The A.G. program, which leads to the A.G. (Accredited Gemologist) Diploma, includes the four core courses:<br> <br />
:E102: Gem Identification<br><br />
:E103: Diamond Grading and Pricing<br><br />
:E201: Colored Stone Grading and Pricing<br><br />
:E301: Synthetic and Treated Gem Identification. <br />
<br />
These 4 courses can be studied in any order, in one or several study periods at AIGS. It is recommended that “Gem Identification” be studied before “Synthethics and Treated Gems”. <br />
<br />
Students enrolling in the entire A.G. program are entitled to a 15% discount off the total tuition fee. Courses must be taken within one year of the first date of payment. Beyond the one year period, students will be subjected to any tuition increases that may have occurred. (Example: Old fee = 20,000 Baht, New fee in effect since date of enrollment = 22,000 Baht, Additional amount to be paid = 2,000 Baht.)<br />
<br />
Living expenses and general overhead are amazingly low compared to countries such as USA, Japan and most of Europe. Students studying at the AIGS can live with a US$600 to US$1000 budget per month including lodging near the school, weekend field trips, restaurants and entertainment. Of course, you can spend much more if you want to, but this amount yields a comfortable lifestyle!<br><br />
Website: http://www.aigsthailand.com/<br />
<br />
====DGemG====<br />
The Deutsche Gemmologische Gesellschaft (The Educational Training Center of the German Gemmological Association) is located in Idar-Oberstein, Germany. Idar-Oberstin is an international colored stone gem capital, where gem cutting has been traditionally mastered for centuries. It is currently bustling with local gem artists and studios. It has, perhaps, the highest per capita population of gem cutters in the world! The German Gemmological Association was founded in 1932.<br />
Its laboratories have modern state of the art equipment, and one of the most extensive colored and exotic gemstone collections available.<br />
<br />
Costs:<br />
<br />
Euro 5,800.00<br />
<br />
====FGAA====<br />
<br />
The Gemmological Association of Australia (GAA), founded in 1945, is Australia’s historic trade-accepted non-profit educational authority for gemmology. <br><br />
They offer gemmological courses in 6 state divisions.<br />
<br />
Costs: contact one of the six state divisions for pricing.<br />
<br />
Website: [http://www.gem.org.au www.gem.org.au]<br />
<br />
====CGA====<br />
<br />
The Canadian Gemmological Association, based in Toronto Canada, is a Canada-wide professional organization which has set the standard for excellence in the practice of gemmology. It was founded in 1958 by Dean S.M. Field, and has since provided training in gemmology to persons dealing with gemstones in the jewellery industry and to hobbyists for better appreciation and possible new career opportunities within gemmology.<br />
<br />
They offer a years correspondence course as well classes on location.<br />
<br />
Costs:<br />
<br />
The two year correspondence course, leading to a Diploma in Gemmology and a Fellowship (FCGmA) in the Canadian Gemmological Association, is offered for CAD 2,020.00<br />
<br />
Webite [http://www.canadiangemmological.com/ canadagemmological.com]<br />
<br />
===Post Graduate===<br />
<br />
After gaining your gemological diploma, the real fun starts. You will know the basics and more importantly you will know how to read the many articles published in various [[periodicals]].<br><br />
If you keep up to date and involved, you will be a good gemologist one day.<br />
<br />
====Career Opportunities====<br />
<br />
As with any profession, it is all up to you what you will become and what your salary will be.<br />
<br />
Think of a gemological diploma as if you have finished your first year in college and the payrate according to that when you start out.<br><br />
You will be qualified to find jobs in gemological laboratories worldwide, be the key figure in the local jewelry store, manager of a tellsell company, start your own gemtrading business, become an appraiser, shoveling municipal gardens etc.<br><br />
Anything you set your mind to.<br />
<br />
Payrate is according to experience, but a starting wage of USD 20,000.00 sounds fair (depending on locality/age/experience ofcourse).<br><br />
Best advice is to start networking from the start and to seek a new employer every few years so you can gain as much know-how as you can.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Introduction_to_Gemology&diff=1561Introduction to Gemology2006-03-05T16:06:53Z<p>Anatase: /* GIA */</p>
<hr />
<div>==General information on Gemology==<br />
<br />
===What is Gemology===<br />
<br />
'''Gemology''' is the science and study of gemstones, which often involves the study of mineralogical fundamentals such as formations, genesis, localities, physical properties and identification of gemstones. It includes the basic knowledge of structural, crystallographic, chemical and physical characteristics and properties of gems. It also involves the way in which gemstones are fashioned.<br />
<br />
''Special Gemology'' deals with categories and varieties of gemstones, synthetic stones and imitations. Conventionally, the organic substances such as amber, pearls, coral and the non-minerals are also included in this subject of special gemology.<br />
<br />
''Practical Gemology'' refers to the application of the knowledge of characteristics and properties of gemstones in identification or separation of synthetics and imitations. Diamond grading is included in practical gemology.<br />
<br />
===What is a Gemologist===<br />
<br />
A gemologist is someone who studies gemstones. Being recognized as a gemologist usually involves having credentials from one of the Institutes for Gem(m)ological Studies discussed below (see '''Becoming a Gemologist''').<br />
<br />
===What are gemstones===<br />
<br />
Gemstones are usually [[mineral]]s but sometimes [[inorganic]] substances.<br />
What separates them from minerals in general is that they are used in jewelry.<br><br />
That is a very thin line of separation, but usually we take 4 factors into account:<br />
<br />
* [[Durability]]<br />
* [[Rarity]]<br />
* [[Beauty]]<br />
* [[Price]]<br />
<br />
And of course the 5th factor:<br />
<br />
* [[Fashion]]<br />
<br />
All the factors above are very subjective, for instance [[Amber]] has very poor durabilty, isn't very rare and in<br />
general is not highly priced. Yet it is considered to be a gem due to its beauty.<br />
On the counterpart, most [[Sapphire]] has good durability but can be very unattractive and cheap. Only a small portion of<br />
all Sapphires mined have good color/beauty.<br />
<br />
==Becoming a Gemologist==<br />
<br />
Becoming a gemologist in general means hard work and commitment. A wise teacher once said "You are only permitted to read books related to our trade and a religious book of your choice from now on . . . for the rest of your life".<br />
<br />
===Education===<br />
<br />
====Gem-A====<br />
<br />
Better known as The Gemmological Association and Gem Testing Laboratory of Great-Britain,<br> <br />
this school is London based with departments worldwide. It offers distance tutoring as well as through teaching centers.<br><br />
The primary focus is on indepth theory and the exams are the hardest to take in the industry. A fellowship of Gem-A means esteem. <br />
<br />
Costs:<br />
<br />
Foundation correspondence course GBP 993.00<br><br />
Diploma correspondence course GBP 1356.00 (on completion is granted the FGA title).<br />
<br />
Gem Diamond diploma course GBP 1584.00 (on completion is granted the DGA title).<br />
<br />
Website http://gem-a.info/<br />
<br />
====GIA====<br />
<br />
The Gemological Institute of America is the most prestigious and respected institute for gemology within the United States. Its main location is in Carlsbad, California, with facilities in New York and Los Angeles. Correspondence courses are available and encouraged. <br />
It was established in 1931, and currently the GIA is the world’s largest and one of the most respected nonprofit institutes of gemological research and learning internationally.<br />
It employs nearly 900, including scientists, diamond graders, and educators.<br />
<br />
Costs:<br />
<br />
On campus (CB/NY/LA): 6 month continuous program (780 hours) $13,995<br />
<br />
Distance Education: GEM130, GEM230, GEM230L, GEM120, GEM220,GEM220L, GEM240, GEM240L (Maximum completion time: 63 months) $6,975 ($7,395 International)<br />
<br />
What you earn: Graduate Gemologist Diploma, Graduate Diamonds Diploma, Graduate Colored Stones Diploma<br><br />
Website: http://www.gia.edu<br />
<br />
====AIGS====<br />
Thailand is in the heart of Southeast Asia 's gem and jewelry production and trading area. It presents you with an extraordinary opportunity to learn gemology in theory and practice while experiencing the gem business in a three dimensional way. <br />
<br />
The A.G. program, which leads to the A.G. (Accredited Gemologist) Diploma, includes the four core courses:<br> <br />
:E102: Gem Identification<br><br />
:E103: Diamond Grading and Pricing<br><br />
:E201: Colored Stone Grading and Pricing<br><br />
:E301: Synthetic and Treated Gem Identification. <br />
<br />
These 4 courses can be studied in any order, in one or several study periods at AIGS. It is recommended that “Gem Identification” be studied before “Synthethics and Treated Gems”. <br />
<br />
Students enrolling in the entire A.G. program are entitled to a 15% discount off the total tuition fee. Courses must be taken within one year of the first date of payment. Beyond the one year period, students will be subjected to any tuition increases that may have occurred. (Example: Old fee = 20,000 Baht, New fee in effect since date of enrollment = 22,000 Baht, Additional amount to be paid = 2,000 Baht.)<br />
<br />
Living expenses and general overhead are amazingly low compared to countries such as USA, Japan and most of Europe. Students studying at the AIGS can live with a US$600 to US$1000 budget per month including lodging near the school, weekend field trips, restaurants and entertainment. Of course, you can spend much more if you want to, but this amount yields a comfortable lifestyle!<br />
<br />
====DGemG====<br />
The Deutsche Gemmologische Gesellschaft (The Educational Training Center of the German Gemmological Association) is located in Idar-Oberstein, Germany. Idar-Oberstin is an international colored stone gem capital, where gem cutting has been traditionally mastered for centuries. It is currently bustling with local gem artists and studios. It has, perhaps, the highest per capita population of gem cutters in the world! The German Gemmological Association was founded in 1932.<br />
Its laboratories have modern state of the art equipment, and one of the most extensive colored and exotic gemstone collections available.<br />
<br />
Costs:<br />
<br />
Euro 5,800.00<br />
<br />
====FGAA====<br />
<br />
The Gemmological Association of Australia (GAA), founded in 1945, is Australia’s historic trade-accepted non-profit educational authority for gemmology. <br><br />
They offer gemmological courses in 6 state divisions.<br />
<br />
Costs: contact one of the six state divisions for pricing.<br />
<br />
Website: [http://www.gem.org.au www.gem.org.au]<br />
<br />
====CGA====<br />
<br />
The Canadian Gemmological Association, based in Toronto Canada, is a Canada-wide professional organization which has set the standard for excellence in the practice of gemmology. It was founded in 1958 by Dean S.M. Field, and has since provided training in gemmology to persons dealing with gemstones in the jewellery industry and to hobbyists for better appreciation and possible new career opportunities within gemmology.<br />
<br />
They offer a years correspondence course as well classes on location.<br />
<br />
Costs:<br />
<br />
The two year correspondence course, leading to a Diploma in Gemmology and a Fellowship (FCGmA) in the Canadian Gemmological Association, is offered for CAD 2,020.00<br />
<br />
Webite [http://www.canadiangemmological.com/ canadagemmological.com]<br />
<br />
===Post Graduate===<br />
<br />
After gaining your gemological diploma, the real fun starts. You will know the basics and more importantly you will know how to read the many articles published in various [[periodicals]].<br><br />
If you keep up to date and involved, you will be a good gemologist one day.<br />
<br />
====Career Opportunities====<br />
<br />
As with any profession, it is all up to you what you will become and what your salary will be.<br />
<br />
Think of a gemological diploma as if you have finished your first year in college and the payrate according to that when you start out.<br><br />
You will be qualified to find jobs in gemological laboratories worldwide, be the key figure in the local jewelry store, manager of a tellsell company, start your own gemtrading business, become an appraiser, shoveling municipal gardens etc.<br><br />
Anything you set your mind to.<br />
<br />
Payrate is according to experience, but a starting wage of USD 20,000.00 sounds fair (depending on locality/age/experience ofcourse).<br><br />
Best advice is to start networking from the start and to seek a new employer every few years so you can gain as much know-how as you can.</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1484Origins of minerals2006-02-28T01:04:03Z<p>Anatase: /* Basic */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
==Igneous (Magmatic) rocks==<br />
<br />
===Basic===<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
<br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===Advanced===<br />
<br />
====Stages of the igneous or magmatic cycle====<br />
<br />
The stages of the igneous or magmatic cycle are as follows:<br />
<br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br />
==Sedimentary rocks==<br />
<br />
===Basic===<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardness and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
==Metamorphic rocks==<br />
<br />
===Basic===<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
# ''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
# ''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
[[Image:geology.gif]]<br />
<br />
==External links==<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=File:Geology.gif&diff=1483File:Geology.gif2006-02-28T01:01:19Z<p>Anatase: </p>
<hr />
<div></div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1451Origins of minerals2006-02-27T15:58:11Z<p>Anatase: /* IGNEOUS(MAGMATIC)ROCKS */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
=IGNEOUS (MAGMATIC) ROCKS=<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
'''The stages of the igneous or magmatic cycle are as follows:''' <br><br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
=SEDIMENTARY ROCKS=<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardness and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
=METAMORPHIC ROCKS=<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1450Origins of minerals2006-02-27T15:57:54Z<p>Anatase: /* IGNEOUS ROCKS */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
=IGNEOUS(MAGMATIC)ROCKS=<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
'''The stages of the igneous or magmatic cycle are as follows:''' <br><br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
=SEDIMENTARY ROCKS=<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardness and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
=METAMORPHIC ROCKS=<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Table_Of_Contents&diff=1449Table Of Contents2006-02-27T04:04:04Z<p>Anatase: </p>
<hr />
<div>This should hold a logical and an easy to navigate content table.<br />
Doesn't matter if the articles are written yet or not.<br />
<br />
Something like:<br />
<br />
#'''Content'''<br />
##[[Introduction to Gemology]]<br />
###[[An Historical Look at our Obsession with Gems]]<br />
##[[Origins of minerals]]<br />
###[[Origins_of_minerals#Igneous_rocks|Igneous rocks]]<br />
###[[Origins_of_minerals#Sedimentary_rocks|Sedimentary rocks]]<br />
###[[Origins_of_minerals#Metamorphic_rock|Metamorphic rocks]]<br />
##[[Chemical Classification of Gems & Gemstones]]<br />
###[[Class I: Pure Elements]]<br />
###[[Class II: Sulphides]]<br />
###[[Class III: Halides]]<br />
###[[Class IV: Oxides]]<br />
###[[Class V a:Carbonates]]<br />
###[[Class V b:Borates]]<br />
###[[Class VI a:Tungstates]]<br />
###[[Class VI b:Sulphates]]<br />
###[[Class VII: Phosphates]]<br />
###[[Class VIII: Silicates]]<br />
###[[Non-Crystalline & Organic Gems]]<br />
##[[Crystal Systems & Forms]]<br />
###[[Crystals & Their Structure]]<br />
####[[Cubic Crystal System]]<br />
####[[Hexagonal Crystal System]]<br />
####[[Tetragonal Crystal System]]<br />
####[[Trigonal Crystal System]]<br />
####[[Rhombic Crystal System]]<br />
####[[Monoclinic Crystal System]]<br />
####[[Triclinic Crystal System]]<br />
##[[Crystallography]]<br />
###[[Naming minerals]]<br />
###[[Symmetry]]<br />
####[[Axis of Symmetry]]<br />
####[[Plane of Symmetry]]<br />
####[[Center of Symmetry]]<br />
###[[Twin Crystals]]<br />
##[[Cleavage]]<br />
###[[Cubic Cleavage]]<br />
###[[Octahedral Cleavage]]<br />
###[[Rhombohedral Cleavage]]<br />
###[[Basal Cleavage]]<br />
###[[Prismatic Cleavage]]<br />
###[[Dodecahedral Cleavage]]<br />
##[[Nature of light]]<br />
###[[Quantum theory]]<br />
###[[Snell's law]]<br />
###[[Polarization]]<br />
<br />
<br />
<br />
etc etc. but then better<br />
<br />
{{footnote}}<br />
<br />
[[category:gemology]]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Table_Of_Contents&diff=1448Table Of Contents2006-02-26T23:32:38Z<p>Anatase: </p>
<hr />
<div>This should hold a logical and an easy to navigate content table.<br />
Doesn't matter if the articles are written yet or not.<br />
<br />
Something like:<br />
<br />
#'''Content'''<br />
##[[Introduction to Gemology]]<br />
###[[An Historical Look at our Obsession with Gems]]<br />
##[[Origins of minerals]]<br />
###[[Origins_of_minerals#Igneous_rocks|Igneous rocks]]<br />
###[[Origins_of_minerals#Sedimentary_rocks|Sedimentary rocks]]<br />
###[[Origins_of_minerals#Metamorphic_rock|Metamorphic rocks]]<br />
##[[Chemical Classification of Gems & Gemstones]]<br />
###[[Class I: Pure Elements]]<br />
###[[Class II: Sulphides]]<br />
###[[Class III: Halides]]<br />
###[[Class IV: Oxides]]<br />
###[[Class V a:Carbonates]]<br />
###[[Class V b:Borates]]<br />
###[[Class VI a:Tungstates]]<br />
###[[Class VI b:Sulphates]]<br />
###[[Class VII: Phosphates]]<br />
###[[Class VIII: Silicates]]<br />
###[[Non-Crystalline & Organic Gems]]<br />
##[[Crystal Systems & Forms]]<br />
###[[Crystals & Their Structure]]<br />
####[[Cubic Crystal System]]<br />
####[[Hexagonal Crystal System]]<br />
####[[Tetragonal Crystal System]]<br />
####[[Trigonal Crystal System]]<br />
####[[Rhombic Crystal System]]<br />
####[[Monoclinic Crystal System]]<br />
####[[Triclinic Crystal System]]<br />
##[[Crystallography]]<br />
###[[Naming minerals]]<br />
###[[Symmetry]]<br />
####[[Axis of Symmetry]]<br />
####[[Plane of Symmetry]]<br />
####[[Center of Symmetry]]<br />
###[[Twin Crystals]]<br />
##[[Cleavage]]<br />
###[[Cubic Cleavage]]<br />
###[[Octahedral Cleavage]]<br />
###[[Rhombohedral Cleavage]]<br />
###[[Basal Cleavage]]<br />
###[[Prismatic Cleavage]]<br />
###[[Dodecahedral Cleavage]]<br />
<br />
##[[Nature of light]]<br />
###[[Quantum theory]]<br />
###[[Snell's law]]<br />
###[[Polarization]]<br />
<br />
<br />
<br />
etc etc. but then better<br />
<br />
{{footnote}}<br />
<br />
[[category:gemology]]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Table_Of_Contents&diff=1447Table Of Contents2006-02-26T23:27:42Z<p>Anatase: </p>
<hr />
<div>This should hold a logical and an easy to navigate content table.<br />
Doesn't matter if the articles are written yet or not.<br />
<br />
Something like:<br />
<br />
#'''Content'''<br />
##[[Introduction to Gemology]]<br />
###[[An Historical Look at our Obsession with Gems]]<br />
##[[Origins of minerals]]<br />
###[[Origins_of_minerals#Igneous_rocks|Igneous rocks]]<br />
###[[Origins_of_minerals#Sedimentary_rocks|Sedimentary rocks]]<br />
###[[Origins_of_minerals#Metamorphic_rock|Metamorphic rocks]]<br />
##[[Chemical Classification of Gems & Gemstones]]<br />
###[[Class I: Pure Elements]]<br />
###[[Class II: Sulphides]]<br />
###[[Class III: Halides]]<br />
###[[Class IV: Oxides]]<br />
###[[Class V a:Carbonates]]<br />
###[[Class V b:Borates]]<br />
###[[Class VI a:Tungstates]]<br />
###[[Class VI b:Sulphates]]<br />
###[[Class VII: Phosphates]]<br />
###[[Class VIII: Silicates]]<br />
###[[Non-Crystalline & Organic Gems]]<br />
##[[Crystal Systems & Forms]]<br />
###[[Crystals & Their Structure]]<br />
####[[Cubic Crystal System]]<br />
####[[Hexagonal Crystal System]]<br />
####[[Tetragonal Crystal System]]<br />
####[[Trigonal Crystal System]]<br />
####[[Rhombic Crystal System]]<br />
####[[Monoclinic Crystal System]]<br />
####[[Triclinic Crystal System]]<br />
##[[Crystallography]]<br />
###[[Naming minerals]]<br />
###[[Symmetry]]<br />
####[[Axis of Symmetry]]<br />
####[[Plane of Symmetry]]<br />
####[[Center of Symmetry]]<br />
##[[Nature of light]]<br />
###[[Quantum theory]]<br />
###[[Snell's law]]<br />
###[[Polarization]]<br />
<br />
<br />
<br />
etc etc. but then better<br />
<br />
{{footnote}}<br />
<br />
[[category:gemology]]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Table_Of_Contents&diff=1446Table Of Contents2006-02-26T23:16:47Z<p>Anatase: </p>
<hr />
<div>This should hold a logical and an easy to navigate content table.<br />
Doesn't matter if the articles are written yet or not.<br />
<br />
Something like:<br />
<br />
#'''Content'''<br />
##[[Introduction to Gemology]]<br />
###[[An Historical Look at our Obsession with Gems]]<br />
##[[Origins of minerals]]<br />
###[[Origins_of_minerals#Igneous_rocks|Igneous rocks]]<br />
###[[Origins_of_minerals#Sedimentary_rocks|Sedimentary rocks]]<br />
###[[Origins_of_minerals#Metamorphic_rock|Metamorphic rocks]]<br />
##[[Chemical Classification of Gems & Gemstones]]<br />
###[[Class I: Pure Elements]]<br />
###[[Class II: Sulphides]]<br />
###[[Class III: Halides]]<br />
###[[Class IV: Oxides]]<br />
###[[Class V a:Carbonates]]<br />
###[[Class V b:Borates]]<br />
###[[Class VI a:Tungstates]]<br />
###[[Class VI b:Sulphates]]<br />
###[[Class VII: Phosphates]]<br />
###[[Class VIII: Silicates]]<br />
###[[Non-Crystalline & Organic Gems]]<br />
##[[Crystallography]]<br />
###[[Naming minerals]]<br />
###[[Symmetry]]<br />
##[[Nature of light]]<br />
###[[Quantum theory]]<br />
###[[Snell's law]]<br />
###[[Polarization]]<br />
<br />
<br />
<br />
etc etc. but then better<br />
<br />
{{footnote}}<br />
<br />
[[category:gemology]]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Table_Of_Contents&diff=1445Table Of Contents2006-02-26T23:15:49Z<p>Anatase: </p>
<hr />
<div>This should hold a logical and an easy to navigate content table.<br />
Doesn't matter if the articles are written yet or not.<br />
<br />
Something like:<br />
<br />
#'''Content'''<br />
##[[Introduction to Gemology]]<br />
###[[An Historical Look at our Obsession with Gems]]<br />
##[[Origins of minerals]]<br />
###[[Origins_of_minerals#Igneous_rocks|Igneous rocks]]<br />
###[[Origins_of_minerals#Sedimentary_rocks|Sedimentary rocks]]<br />
###[[Origins_of_minerals#Metamorphic_rock|Metamorphic rocks]]<br />
##[[Chemical Classification of Gems & Gemstones]]<br />
###[[Class I: Pure Elements]]<br />
###[[Class II: Sulphides]]<br />
###[[Class III: Halides]]<br />
###[[Class IV: Oxides]]<br />
###[[Class Va:Carbonates]]<br />
###[[Class Vb:Borates]]<br />
###[[Class VIa:Tungstates]]<br />
###[[Class VIb:Sulphates]]<br />
###[[Class VII: Phosphates]]<br />
###[[Class VIII: Silicates]]<br />
###[[Non-Crystalline & Organic Gems]]<br />
##[[Crystallography]]<br />
###[[Naming minerals]]<br />
###[[Symmetry]]<br />
##[[Nature of light]]<br />
###[[Quantum theory]]<br />
###[[Snell's law]]<br />
###[[Polarization]]<br />
<br />
<br />
<br />
etc etc. but then better<br />
<br />
{{footnote}}<br />
<br />
[[category:gemology]]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1444Origins of minerals2006-02-26T22:59:45Z<p>Anatase: /* SEDIMENTARY ROCKS */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
=IGNEOUS ROCKS=<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
=SEDIMENTARY ROCKS=<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardness and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
=METAMORPHIC ROCKS=<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1441Origins of minerals2006-02-26T22:23:01Z<p>Anatase: /* <u>METAMORPHIC ROCKS</u> */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
=IGNEOUS ROCKS=<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
=SEDIMENTARY ROCKS=<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
=METAMORPHIC ROCKS=<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1440Origins of minerals2006-02-26T22:22:29Z<p>Anatase: /* <u>SEDIMENTARY ROCKS</u> */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
=IGNEOUS ROCKS=<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
=SEDIMENTARY ROCKS=<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
===<u>METAMORPHIC ROCKS</u>===<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1439Origins of minerals2006-02-26T22:22:09Z<p>Anatase: /* <u>IGNEOUS ROCKS</u> */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
=IGNEOUS ROCKS=<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===<u>SEDIMENTARY ROCKS</u>===<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
===<u>METAMORPHIC ROCKS</u>===<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Table_Of_Contents&diff=1438Table Of Contents2006-02-26T22:20:15Z<p>Anatase: </p>
<hr />
<div>This should hold a logical and an easy to navigate content table.<br />
Doesn't matter if the articles are written yet or not.<br />
<br />
Something like:<br />
<br />
#'''Content'''<br />
##[[Introduction to Gemology]]<br />
###[[An Historical Look at our Obsession with Gems]]<br />
##[[Origins of minerals]]<br />
###[[Origins_of_minerals#Igneous_rocks|Igneous rocks]]<br />
###[[Origins_of_minerals#Sedimentary_rocks|Sedimentary rocks]]<br />
###[[Origins_of_minerals#Metamorphic_rock|Metamorphic rocks]]<br />
##[[Classification of Gems & Gemstones]]<br />
###[[Pure Elements]]<br />
###[[Sulphides]]<br />
###[[Halides]]<br />
###[[Oxides]]<br />
###[[Carbonates]]<br />
###[[Phosphates]]<br />
###[[Silicates]]<br />
###[[Non-Crystalline & Organic Gems]]<br />
##[[Crystallography]]<br />
###[[Naming minerals]]<br />
###[[Symmetry]]<br />
##[[Nature of light]]<br />
###[[Quantum theory]]<br />
###[[Snell's law]]<br />
###[[Polarization]]<br />
<br />
<br />
<br />
etc etc. but then better<br />
<br />
{{footnote}}<br />
<br />
[[category:gemology]]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1437Origins of minerals2006-02-26T21:37:27Z<p>Anatase: /* Metamorphic rock */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
===<u>IGNEOUS ROCKS</u>===<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===<u>SEDIMENTARY ROCKS</u>===<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
===<u>METAMORPHIC ROCKS</u>===<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1436Origins of minerals2006-02-26T21:36:47Z<p>Anatase: /* Sedimentary rocks */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
===<u>IGNEOUS ROCKS</u>===<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===<u>SEDIMENTARY ROCKS</u>===<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
===Metamorphic rock===<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1435Origins of minerals2006-02-26T21:35:50Z<p>Anatase: /* Igneous rocks */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
===<u>IGNEOUS ROCKS</u>===<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. <u>Early Magmatic Phase</u> (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. <u>Liquid Magmatic Phase: </u> (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. <u>Pegmatite Phase </u>(rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. <u>Pneumatolytic Phase:</u> 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. <u>Hydrothermal Phase: </u>400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools:<br><br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===Sedimentary rocks===<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
===Metamorphic rock===<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1434Origins of minerals2006-02-26T21:23:47Z<p>Anatase: /* Igneous rocks */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
===Igneous rocks===<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
<br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. Early Magmatic Phase (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. Liquid Magmatic Phase (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. Pegmatite Phase (rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. Pneumatolytic Phase: 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. Hydrothermal Phase: 400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br />
<br><br><br />
Igneous rocks can further be divided in two types, depending on where the magma cools.<br><br />
<br />
<br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===Sedimentary rocks===<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
===Metamorphic rock===<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1433Origins of minerals2006-02-26T21:08:42Z<p>Anatase: /* Metamorphic rock */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
===Igneous rocks===<br />
<br />
By the cooling down of magma, atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
Igneous rock are divided in two types, depending on where the magma cools.<br><br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. Early Magmatic Phase (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. Liquid Magmatic Phase (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. Pegmatite Phase (rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. Pneumatolytic Phase: 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. Hydrothermal Phase: 400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br />
<br><br><br />
<br />
<br />
<br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===Sedimentary rocks===<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
===Metamorphic rock===<br />
<br />
The metamorphic cycle is the third largest cycle in mineral and rock formation. Metamorphism is the alteration of mineral parageneses after their deposition, by external action such as contact with magmetic rocks, regional changes in the pressure and temperature (e.g. contact metamorphosed limestones, crystalline schists, etc.). The consolidated rocks are altered in composition, texture or internal structure through pressure, heat and new chemical substances.<br><br />
There are two kinds of metamorphism:<br><br />
'''Regional''' and '''Contact''' <br><br />
''Regional metamorphism'' is caused due to a rise in temperature and directed pressure, effecting the earth's crust.<br><br />
''Contact metamorphism'' is caused when magma is intruded into a preexisting rock mass. The heat and pressure of this magma, causes a metamorphic change in the rock it intrudes.<br />
<br />
<br />
Both igneous and sedimentary rocks can change in texture or chemical composition as the result of either contact or regional metamorphism. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
*Alexandrite<br />
*Andaluscite<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1431Origins of minerals2006-02-26T20:45:46Z<p>Anatase: /* Sedimentary rocks */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
===Igneous rocks===<br />
<br />
By the cooling down of magma, atoms are eveated.<br><br />
The atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
Igneous rock are divided in two types, depending on where the magma cools.<br><br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. Early Magmatic Phase (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. Liquid Magmatic Phase (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. Pegmatite Phase (rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. Pneumatolytic Phase: 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. Hydrothermal Phase: 400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br />
<br><br><br />
<br />
<br />
<br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===Sedimentary rocks===<br />
<br />
The Sedimentary cycle is the second largest cycle in mineral and rock formation. These are formed by erosion, transport in rivers, ice etc. and involve the decay and disintegration of a pre-existing rock mass.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
*Malachite<br />
*Azurite<br />
*Chrysoprase<br />
*Chrysocolla<br />
<br />
===Metamorphic rock===<br />
<br />
These are generated by reactions between minerals caused by change in temperature and/or pressure in the earthcrust.<br />
<br />
When earth movements occur, or when magma forces its way into excisting rocks, igneous and sedimentary rocks can change in texture or chemical composition. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1430Origins of minerals2006-02-26T20:38:24Z<p>Anatase: /* Igneous rocks */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
===Igneous rocks===<br />
<br />
By the cooling down of magma, atoms are eveated.<br><br />
The atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
Igneous rock are divided in two types, depending on where the magma cools.<br><br />
'''The stages of the magmatic cycle are as follows:''' <br><br />
1. Early Magmatic Phase (early crystalization) from the firey hot magma:<br><br />
*Chromite<br />
*Magnetite<br />
*Titanium magnetite<br />
2. Liquid Magmatic Phase (main crystallization) 1500-600 degrees C<br />
*Spinel<br />
*Zircon<br />
*Apatite<br />
*Peridot<br />
*Diamond<br />
3. Pegmatite Phase (rest crystllization) 700-400 degrees C <br><br />
The residual part of the magma which is rich in fluxes is known as the pegmatite stage. The melt becomes a watery solution as the solidification proceeds. Because of this fluidity, the liquids can penetrate fissures and cracks in the surrounding rocks. Under the concentrated pressure and temperatures, individual crytals form that can measure several centimeters and occasionally, several meters! The prismatic crystals grow perpendicular to the walls of the vein. Pegmatite veins are some of the best examples of gemstone formation.<br />
*Tourmaline<br />
*Beryl<br />
*Quartz<br />
*Feldspar<br />
*Zircon<br />
*Apatite<br />
*Brazillianite<br />
*Graphite<br />
*Muscovite<br />
*Lepidolite<br />
4. Pneumatolytic Phase: 500-300 degrees C <br><br />
Minerals formed in this phase, form at lower temperatures and rising pressure. Superheated volatile components are involved. The most prominent of these components is water vapor, boron and fluorine gasses. Under the influence of these vapors, other minerals are often formed in the contact zone of limestone. <br><br />
*Topaz<br />
*Euclase<br />
*Vesuvianite<br />
*Fluorite<br />
*Cassiterite<br />
*Sheelite<br />
*Wolframite<br />
5. Hydrothermal Phase: 400- 50 degrees C <br><br />
This is a process associated with igneous activity that involves heated or super-heated water. Water at very high temperature and pressure is an exceedingly active substance, capable of breaking down silicates and dissolving many substances normally thought to be insoluble. This is the last stage of minerals that can be considered to be formed directly from magma.<br />
*Gold<br />
*Silver<br />
*Emerald (Colombian)<br />
*Beryl<br />
*Quartz<br />
*Baryte<br />
*Pyrite<br />
*Dolomite<br />
*Calcite<br />
<br />
<br><br><br />
<br />
<br />
<br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===Sedimentary rocks===<br />
<br />
These are formed by erosion, transport in rivers, ice etc. snd desposition of other rocks.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands or clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are found in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals are carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and density many diamonds survive the sedimentary processes and are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
<br />
===Metamorphic rock===<br />
<br />
These are generated by reactions between minerals caused by change in temperature and/or pressure in the earthcrust.<br />
<br />
When earth movements occur, or when magma forces its way into excisting rocks, igneous and sedimentary rocks can change in texture or chemical composition. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel<br />
<br />
===External links===<br />
<br />
[http://www.physicalgeography.net/fundamentals/chapter10.html FUNDAMENTALS OF PHYSICAL GEOGRAPHY]</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Polarization&diff=1425Polarization2006-02-26T17:31:37Z<p>Anatase: /* Polariscope */</p>
<hr />
<div>Polarization is a concept that is easy to comprehent and plays a key role in many concepts that are important to us <br />
gemologists.<br><br />
Understanding the basics of it is vital in your studies.<br />
<br />
==Basics==<br />
<br />
[[image:spherical.png|right|thumb|Sphercial light]]<br />
<br />
Light from the sun or a lightbulb is spherical. Meaning that it transmits light in all directions.<br><br />
If you would follow one lightray in one direction (the direction of propogandation) it can be seen as a circle with <br />
light being transmitted at a 90° angle to that direction. Something which we call transversal light. <br />
<br />
It is this transversal light that we use as illustration for polarized light.<br />
<br />
[[image:transversal.png|left|thumb|Transversal light]]<br />
<br />
<br />
A polarization filter only lets through light which vibrates in one direction depending on its orientation.<br><br />
Imagine a lightsource traveling towards a wall. When it reaches the wall no light can pass through it. If you would cut <br />
horizontal slices out of the wall the effect would be a Venetian blinds effect on the other side of the wall.<br />
<br />
The same happens with polarizing filters. They are manufactured in a way that only a specific wave of transversal light <br />
can pass through the filter.This has wide use, from sunglasses to [[conoscopy]] and many more.<br />
<br clear=all><br />
<br />
[[image:polarizer.png|right|thumb|Crossed polarization filters]]<br />
<br />
<br />
If you would position the polarisation filter in North-South position only waves in the N-S position are able to pass <br />
through the filter. On rotation of the filter other orientations will pass through.<br><br />
This is what we call "plane polarized light".<br />
<br />
When two filters are used and they are orientated in opposite directions, no light can pass at the end because one is <br />
in N-S position (letting only the N-S waves to pass) and the other is in East-West. When that light wave reaches the <br />
second filter that 2nd filter will only let waves in East-West position pass. Which is not there. <br />
Thus it will block the remaining North-South lightwave as can be seen on the image on the right.<br />
<br clear=all><br />
<br />
[[image:transversalNS.png|left|thumb|Transversal light with light wave in N-S direction]]<br />
<br />
<br />
This feature can be helpfull when combined with previous knowledge of [[double refraction]].<br clear=all><br />
<br />
[[Anisotropic]] minerals have the ability to split light into two rays.<br><br />
This is due to their moluclar stacking and some other reasons.<br><br />
As a result the two different rays travel through the gemstone at different velocities and they vibrate at right angles <br />
to eachother.<br />
<br />
--illustration--<br />
<br />
===Polariscope===<br />
<br />
[[Image:Polariscope.jpg]]<br />
<br />
A polariscope uses polarized light for gem identification. It consists of two polarized filters, one on the top and one on the bottom of the instrument as seen in the above picture. Both the polariser and the analyser have their own vibrational planes. When the vibrational plane of the polarizer is at right angles to the vibrational direction of the analyser, the field between them remains dark. This position is known as the "crossed position". In this position, gems can be tested to determine if they are:<br><br />
*Isotropic <br><br />
*Anisotropic<br><br />
*Anamolously Double Refractive or an<br><br />
*Anisotropic Aggregate<br><br />
The polarising filters in this instrument are made of a plastic with microscopically oriented crystals of quinine idosulphate.<br />
<br />
==Advanced==<br />
<br />
content needed<br />
<br />
===Conoscopy===<br />
<br />
<br />
[http://users.skynet.be/jm-derochette/conoscopy.htm Conoscopy Illustrated]<br />
<br />
==Expert==<br />
<br />
content needed<br />
<br />
===Retardation===<br />
<br />
content needed<br />
<br />
===Elipsoids===<br />
<br />
content needed</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1422Origins of minerals2006-02-26T16:33:49Z<p>Anatase: /* Volcanic or extrusive rock */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
===Igneous rocks===<br />
<br />
By the cooling down of magma, atoms are eveated.<br><br />
The atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
Igneous rock are divided in two types, depending on where the magma cools.<br />
<br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
*Snowflake Obsidian ( with inclusions of the mineral cristobalite)<br><br />
*Rainbow Obsidian <br><br />
*Red Mahogany Obsidian <br><br />
*Silver Sheen Obsidian <br> <br />
*Midnight Lace Obsidian<br> <br />
*Pumpkin Obsidian <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===Sedimentary rocks===<br />
<br />
These are formed by erosion, transport in rivers, ice etc. snd desposition of other rocks.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands oe clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are form in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals sre carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and tensity many diamonds survive the sedimentary processesand are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
<br />
===Metamorphic rock===<br />
<br />
These are generated by reactions between minerals caused by change in temperature and/or pressure in the earthcrust.<br />
<br />
When earth movements occur, or when magma forces its way into excisting rocks, igneous and sedimentary rocks can change in texture or chemical composition. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Origins_of_minerals&diff=1421Origins of minerals2006-02-26T16:31:38Z<p>Anatase: /* Volcanic or extrusive rock */</p>
<hr />
<div>There are, in principle, three types of rocks and minerals are part of those.<br />
<br />
===Igneous rocks===<br />
<br />
By the cooling down of magma, atoms are eveated.<br><br />
The atoms are linked into crystalline patterns and subsequently different minerals are formed.<br />
<br><br />
When the formation takes place in the depths of the earthcrust (approx. 33km deep) quite large rocks may be formed (for instance granites).<br />
<br />
Igneous rocks are formed and created by magmatic processes in the earth. To form very large crystals of rare minerals, exceptional conditions are needed.<br />
<br />
For instance a rock called pegmatite, which is formed by the crystallisation of magma enriched with water in the veins of other rocks. They may contain Beryl, Tourmaline and Topaz.<br />
<br />
Igneous rock are divided in two types, depending on where the magma cools.<br />
<br />
====Volcanic or extrusive rock====<br />
<br />
This is rock that is formed on the surface of the earth.<br><br />
In contact with air, or seawater, molten rock cools rapidly and either quenches to a glass (like Obsidian) or it forms small crystals (basalt).<br />
<br />
Volcanic rocks are usually finely grained or glassy in structure.<br><br />
Basalt is an extrusive rock and is finely grained due to its rapid cooling. It largely consists of tiny Feldspar and pyroxene crystals (like Diopside and Enstatite).<br><br />
Some basalts contain gemstones like Corundum, Zircon and Garnets.<br />
<br />
Another volcanic rock is called Kimberlite and some of the kimberlite pipes are the major source of Diamond.<br />
<br />
Occasionally, varieties of volcanic glass, [http://www.cst.cmich.edu/users/dietr1rv/obsidian.htm Obsidian], are cut and fashioned as gemstones. It is an amorphous mineraloid with the hardness of approximately 5.5. Varieties include:<br><br />
'''Snowflake Obsidian''' ( with inclusions of the mineral cristobalite)<br><br />
'''Rainbow Obsidian''' <br><br />
'''Red Mahogany Obsidian''' <br><br />
'''Silver Sheen Obsidian''' <br> <br />
'''Midnight Lace Obsidian'''<br> <br />
'''Pumpkin Obsidian''' <br><br />
<br />
====Plutonic or intrusive rock====<br />
<br />
When the molten rock solidifies below the earth's surface, it cools slowly and it forms plutonic rocks with larger crystals. They tend to be coarser grained.<br />
<br />
Granite is a coarse grained intrusive rock containg the minerals Quartz and Feldspar, usually with Mica or Hornblade.<br />
In some circumstances granite undergoes "fractional crystallisation": during slow cooling different minerals may form at different temperatures. Among the last to be formed, often in veins penetrating the surrounding, are minerals of the Pegmatite group.<br />
<br />
Associated minerals that find their origin in igneous rocks:<br />
<br />
*Beryl<br />
*Chrysoberyl<br />
*Corundum<br />
*Diamond<br />
*Garnet<br />
*Feldspar<br />
*Peridot<br />
*Quartz<br />
*Spinel<br />
*Topaz<br />
*Tourmaline<br />
*Zircon<br />
<br />
===Sedimentary rocks===<br />
<br />
These are formed by erosion, transport in rivers, ice etc. snd desposition of other rocks.<br><br />
Usually there are no new minerals formed, only found.<br />
<br />
When these particels eventually settle, they form alluvial gravels, sands oe clays. When they are either cemented or compressed, then they form sedimentary rocks such a conglomerations, sandstones and limestones.<br />
<br />
Chemical action in the environment leads to some material dissolving in water. Eventually the water may evaporate and desposits of Borax and other salt "evaporites" may form this way.<br />
<br />
Plant and animal remains are commonly incorporated among the rock fragments and these may be preserved as fossils.<br />
<br />
Many gemstones are form in "alluvial deposits".<br><br />
These deposits have their origin in the destruction of the origional rocks and the resulting materials by rivers, floods and glacial movement.<br />
During this movement the heavier minerals tend to remain relatively close to the source, whilst lighter minerals sre carried further away.<br><br />
The heavier and harder materials do not wear as much as the lighter ones and tend to retain more of their crystal shape.<br><br />
Stones as Sapphire and Topaz do not show as much abrasion as softer minerals like Quartz.<br />
<br>However due to the continious grinding and tumbling over a period of time a large number of gem minerals are found a rounded "water-worn" pebbles.<br />
The gem gravels in Sri Lanka contain a wide variety of such minerals.<br><br />
Because of their supreme hardnes and tensity many diamonds survive the sedimentary processesand are frequently found in alluvial deposits.<br />
<br />
Minerals found in sedimentary rocks:<br />
<br />
*Beryl<br />
*Opal<br />
*Quartz<br />
*Turquoise<br />
<br />
===Metamorphic rock===<br />
<br />
These are generated by reactions between minerals caused by change in temperature and/or pressure in the earthcrust.<br />
<br />
When earth movements occur, or when magma forces its way into excisting rocks, igneous and sedimentary rocks can change in texture or chemical composition. Thus excisting rocks change into new types of rocks.<br><br />
They are usually harder and denser than the origional material.<br />
<br />
For example shale may alter into slateand by further metamorphose into schist. Limestone is converted into marble.<br><br />
Sometimes schists contain gem minerals like Garnet, Emerald and Corundum.<br />
<br />
Some minerals that grow in metamorhic rocks are:<br />
<br />
*Beryl<br />
*Corundum<br />
*Danburite<br />
*Garnets<br />
*Iolite<br />
*Lapis Lazuli<br />
*Jadeite<br />
*Nephrite<br />
*Spinel</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Polarization&diff=1415Polarization2006-02-26T03:57:41Z<p>Anatase: /* Conoscopy */</p>
<hr />
<div>Polarization is a concept that is easy to comprehent and plays a key role in many concepts that are important to us <br />
gemologists.<br><br />
Understanding the basics of it is vital in your studies.<br />
<br />
==Basics==<br />
<br />
[[image:spherical.png|right|thumb|Sphercial light]]<br />
<br />
Light from the sun or a lightbulb is spherical. Meaning that it transmits light in all directions.<br><br />
If you would follow one lightray in one direction (the direction of propogandation) it can be seen as a circle with <br />
light being transmitted at a 90° angle to that direction. Something which we call transversal light. <br />
<br />
It is this transversal light that we use as illustration for polarized light.<br />
<br />
[[image:transversal.png|left|thumb|Transversal light]]<br />
<br />
<br />
A polarization filter only lets through light which vibrates in one direction depending on its orientation.<br><br />
Imagine a lightsource traveling towards a wall. When it reaches the wall no light can pass through it. If you would cut <br />
horizontal slices out of the wall the effect would be a Venetian blinds effect on the other side of the wall.<br />
<br />
The same happens with polarizing filters. They are manufactured in a way that only a specific wave of transversal light <br />
can pass through the filter.This has wide use, from sunglasses to [[conoscopy]] and many more.<br />
<br clear=all><br />
<br />
[[image:polarizer.png|right|thumb|Crossed polarization filters]]<br />
<br />
<br />
If you would position the polarisation filter in North-South position only waves in the N-S position are able to pass <br />
through the filter. On rotation of the filter other orientations will pass through.<br><br />
This is what we call "plane polarized light".<br />
<br />
When two filters are used and they are orientated in opposite directions, no light can pass at the end because one is <br />
in N-S position (letting only the N-S waves to pass) and the other is in East-West. When that light wave reaches the <br />
second filter that 2nd filter will only let waves in East-West position pass. Which is not there. <br />
Thus it will block the remaining North-South lightwave as can be seen on the image on the right.<br />
<br clear=all><br />
<br />
[[image:transversalNS.png|left|thumb|Transversal light with light wave in N-S direction]]<br />
<br />
<br />
This feature can be helpfull when combined with previous knowledge of [[double refraction]].<br clear=all><br />
<br />
[[Anisotropic]] minerals have the ability to split light into two rays.<br><br />
This is due to their moluclar stacking and some other reasons.<br><br />
As a result the two different rays travel through the gemstone at different velocities and they vibrate at right angles <br />
to eachother.<br />
<br />
--illustration--<br />
<br />
===Polariscope===<br />
<br />
[[Image:Polariscope.jpg]]<br />
<br />
A polariscope uses polarized light for gem identification. It consists of two polarized filters, one on the top and one on the bottom of the instrument as seen in the above picture. Both the polariser and the analyser have their own vibrational planes. When the vibrational plane of the polarizer is at right angles to the vibrational direction of the analyser, the field between them remains dark. This position is known as the "crossed position". In this position, gems can be tested to determine if they are:<br><br />
'''Isotropic''' <br><br />
'''Anisotropic'''<br><br />
'''Anamolously Double Refractive''' or an<br><br />
'''Anisotropic Aggregate'''<br><br />
The polarising filters in this instrument are made of a plastic with microscopically oriented crystals of quinine idosulphate.<br />
<br />
==Advanced==<br />
<br />
content needed<br />
<br />
===Conoscopy===<br />
<br />
<br />
[http://users.skynet.be/jm-derochette/conoscopy.htm Conoscopy Illustrated]<br />
<br />
==Expert==<br />
<br />
content needed<br />
<br />
===Retardation===<br />
<br />
content needed<br />
<br />
===Elipsoids===<br />
<br />
content needed</div>Anatasehttp://gemologyproject.com/wiki/index.php?title=Polarization&diff=1414Polarization2006-02-26T03:14:57Z<p>Anatase: /* Polariscope */</p>
<hr />
<div>Polarization is a concept that is easy to comprehent and plays a key role in many concepts that are important to us <br />
gemologists.<br><br />
Understanding the basics of it is vital in your studies.<br />
<br />
==Basics==<br />
<br />
[[image:spherical.png|right|thumb|Sphercial light]]<br />
<br />
Light from the sun or a lightbulb is spherical. Meaning that it transmits light in all directions.<br><br />
If you would follow one lightray in one direction (the direction of propogandation) it can be seen as a circle with <br />
light being transmitted at a 90° angle to that direction. Something which we call transversal light. <br />
<br />
It is this transversal light that we use as illustration for polarized light.<br />
<br />
[[image:transversal.png|left|thumb|Transversal light]]<br />
<br />
<br />
A polarization filter only lets through light which vibrates in one direction depending on its orientation.<br><br />
Imagine a lightsource traveling towards a wall. When it reaches the wall no light can pass through it. If you would cut <br />
horizontal slices out of the wall the effect would be a Venetian blinds effect on the other side of the wall.<br />
<br />
The same happens with polarizing filters. They are manufactured in a way that only a specific wave of transversal light <br />
can pass through the filter.This has wide use, from sunglasses to [[conoscopy]] and many more.<br />
<br clear=all><br />
<br />
[[image:polarizer.png|right|thumb|Crossed polarization filters]]<br />
<br />
<br />
If you would position the polarisation filter in North-South position only waves in the N-S position are able to pass <br />
through the filter. On rotation of the filter other orientations will pass through.<br><br />
This is what we call "plane polarized light".<br />
<br />
When two filters are used and they are orientated in opposite directions, no light can pass at the end because one is <br />
in N-S position (letting only the N-S waves to pass) and the other is in East-West. When that light wave reaches the <br />
second filter that 2nd filter will only let waves in East-West position pass. Which is not there. <br />
Thus it will block the remaining North-South lightwave as can be seen on the image on the right.<br />
<br clear=all><br />
<br />
[[image:transversalNS.png|left|thumb|Transversal light with light wave in N-S direction]]<br />
<br />
<br />
This feature can be helpfull when combined with previous knowledge of [[double refraction]].<br clear=all><br />
<br />
[[Anisotropic]] minerals have the ability to split light into two rays.<br><br />
This is due to their moluclar stacking and some other reasons.<br><br />
As a result the two different rays travel through the gemstone at different velocities and they vibrate at right angles <br />
to eachother.<br />
<br />
--illustration--<br />
<br />
===Polariscope===<br />
<br />
[[Image:Polariscope.jpg]]<br />
<br />
A polariscope uses polarized light for gem identification. It consists of two polarized filters, one on the top and one on the bottom of the instrument as seen in the above picture. Both the polariser and the analyser have their own vibrational planes. When the vibrational plane of the polarizer is at right angles to the vibrational direction of the analyser, the field between them remains dark. This position is known as the "crossed position". In this position, gems can be tested to determine if they are:<br><br />
'''Isotropic''' <br><br />
'''Anisotropic'''<br><br />
'''Anamolously Double Refractive''' or an<br><br />
'''Anisotropic Aggregate'''<br><br />
The polarising filters in this instrument are made of a plastic with microscopically oriented crystals of quinine idosulphate.<br />
<br />
==Advanced==<br />
<br />
content needed<br />
<br />
===Conoscopy===<br />
<br />
content needed<br />
<br />
==Expert==<br />
<br />
content needed<br />
<br />
===Retardation===<br />
<br />
content needed<br />
<br />
===Elipsoids===<br />
<br />
content needed</div>Anatase