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5.2: Crystal Systems

Last updated

May 6, 2022
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- 5.1: Crystallography
- 5.3: Form

gemology
Gemology Project

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Table $\PageIndex{1}$ : Table of Crystal Systems

Crystal System	Diagram	Examples
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.		Diamond Garnet Spinel
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.		Zircon
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).		Aquamarine Beryl Emerald Heliodor Morganite Apatite
Trigonal The trigonal system is a subsystem of the hexagonal system according to some institutes, therefore some gem references will list these as hexagonal.		Amethyst Benitoite Citrine Corundum Quartz Ruby Sapphire Tourmaline
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.		Alexandrite Andalusite Chrysoberyl Iolite Peridot Tanzanite Topaz Varisite
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. You can imagine this as a matchbox that slants to one side.		Azurite Diopside Feldspar Kunzite Nephrite
Triclinic In this system all the axes are different lengths and none of them meet at 90°. You can imagine this as a matchbox which slants to two sides.		Turquoise

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