From The Gemology Project
Crystal Systems & Forms
Crystal System
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Diagram
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Examples
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Cubic
The cube is composed of 6 square faces
at 90 degree angles to each other. Each
face intersects one of the crystallographic
axes and is parallel to the other two.
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Diamond
Garnet
Spinel
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Tetragonal
The tetragonal system also has three axes
that all meet at 90°. It differs from the
isometric system in that the C axis is longer
than the A and B axis which are the same length
that all meet at 90°. It differs from the isometric
system in that the C axis is longer than the A
and B axis which are the same length.
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Zircon
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Hexagonal
In the hexagonal system we have an additional axes,
which gives the crystals six sides. Three of these
are equal in length and meet at 60° to each other.
The C or vertical axis is at 90° to the shorter axes.
Mineralogists sometimes divide this into two systems,
the hexagonal and the trigonal, based on their external
appearance, as follows:
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Aquamarine
Benitoite
Beryl
Citrine
Emerald
Heliodor
Morganite
Quartz
Ruby
Sapphire
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Trigonal
Again, the trigonal system is a subsystem of the
hexagonal. Most gem references will list these as
hexagonal.
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Amethyst
Corundum
Tourmaline
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Orthorhombic
In this system there are three axes, all of which
meet at 90° to each other. However, all the axes
are a different length.
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Alexandrite
Andalusite
Chrysoberyl
Iolite
Peridot
Tanzanite
Topaz
Varisite
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Monoclinic
The above crystal systems all have axes sides
that meet at 90°. In the monoclinic system all
the axes are different lengths. Two of them,
the A and C axes, meet at 90°, but the third
one does not
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Azurite
Diopside
Feldspar
Kunzite
Nephrite
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Triclinic
In this system all the axes are different
lengths and none of them meet at 90°.
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Turquoise
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