Difference between revisions of "Sphene"
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==Varieties== | ==Varieties== | ||
− | Chrome sphene, intense green (color cause by chromium). | + | *Chrome sphene, intense green (color cause by chromium). |
+ | *Greenovite, a reddish variety owning its color to manganese (MnO) impurities. | ||
==Occurence== | ==Occurence== |
Revision as of 11:33, 31 May 2007
Sphene | |
---|---|
Chemical composition | CaTiOSiO4 |
Crystal system | Monoclinic |
Habit | Wedge shaped, massive |
Cleavage | Distinct, prismatic |
Fracture | Conchoidal |
Hardness | 5.0-5.5 |
Optic nature | Biaxial + |
Refractive index | 1.880-2.099 |
Birefringence | 0.100-0.135 |
Dispersion | High, 0.051 |
Specific gravity | 3.45-3.55 |
Lustre | Resinous to sub-adamantine |
Pleochroism | Distinct to strong |
Sphene is the older name of this mineral wich refers to its crystalshape. Titanite is the universial name amongst mineralogists today and refers to its content of titanium. Greenovite is the name given to red or pink sphene. Gemologists use the name sphene for gem material titanite.
Sphene is isostructural with tilasite, malayaite and fersmantite.
Contents
Diagnostics
Color
Yellow, brown, green, reddish.
Color is caused by rare earth elements (didymium) for yellow stones and chromium for the intense green chrome sphene.
Streak
White.
Diaphaneity
Transparent to opaque.
Refractometer
nα = 1.843 - 1.950, nβ = 1.870 - 2.034, nγ = 1.943 - 2.110 with a birefringence of 0.100 - 0.192.
Optical nature: biaxial positive.
A strong doubling of facets is seen in cut stones.
Polariscope
Due to its small to moderate 2V value (17-40°) a clear biaxial interference pattern may be seen (two melatopes visible in one image).
Pleochroism
Moderate to strong trichroism.
Yellow to brown stones: colourless, greenish-yellow, reddish.
Spectroscope
Sometimes a spectrum can be seen.
Mean absorption lines: 586, 582. Sphene may show (weak) rare earth spectra due to didymium.
Fluorescence
None (probably due to iron content).
Varieties
- Chrome sphene, intense green (color cause by chromium).
- Greenovite, a reddish variety owning its color to manganese (MnO) impurities.
Occurence
Sphene is a common and widespread mineral in many igneous rocks and metamorphic rocks. Associated minerals are pyroxene, amphibole, feldspar and quartz.
Habit
Wedge-shaped crystals that may show parting due to twinning. Less common massive or lamellar. Sphene is normally fine grained but occacionally forms large crystals.
Sphene may show some degree of metamictization.
Treatments
Sphene is changed to red or orange through heating.
Durability
Sphene's relative low hardness makes it vulnerable to abbrasion.
Deposits
Myanmar, Sri Lanka, Brazil, Mexico, Russia and Austria
Sources
- Gems sixth edition (2006) - Michael O'Donoghue ISBN 0750658568
- Gemstones of the world, 3rd rev and exp edition (2006) - Walter Schuman ISBN 1402740166
- Mineralogy second edition (2002) - Dexter Perkins ISBN 0130620998
- Introduction to Optical Mineralogy (2004) - William D. Nesse ISBN 0195149106
- Gemmology 3rd edition (2005) - Peter G. Read ISBN 0750664495
- Gem Reference Guide (1995) - GIA ISBN 0873110293