| Crystal Systems |
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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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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. |
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 Zircon |
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. |
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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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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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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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Triclinic In this system all the axes are different lengths and none of them meet at 90°. |
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 Turquoise |
Diamond
Garnet 
Rhodolite 
Spinel
Aquamarine
Benitoite
Beryl 
Emerald
Heliodor
Morganite
Amethyst
Citrine 
Corundum
Ruby 
Sapphire
Tourmaline
Quartz
Alexandrite
Andalusite
Chrysoberyl
Iolite 
Peridot 
Tanzanite 
Topaz 
Azurite
Diopside
Feldspar
Kunzite
Nephrite