From The Gemology Project
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° 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 or
shorter than the A axes,
which are the same length.
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Zircon
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Hexagonal
In the hexagonal system, we have an additional axis,
giving the crystals six sides. Three of these
are equal in length and meet at 120° to each other.
The C or vertical axis is at 90° to the horizontal axes.
Mineralogists sometimes divide this into two systems,
the hexagonal and the trigonal, based on their external
appearance (see following).
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Aquamarine
Beryl
Emerald
Heliodor
Morganite
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Trigonal
The trigonal system is a subsystem of the
hexagonal system according to some institutes,
therefore some gem references will list these as
hexagonal.
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Amethyst
Benitoite
Citrine
Corundum
Quartz
Ruby
Sapphire
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 of 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. The A axis is inclined
to the C axis. The B axis is at 90° to them.
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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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