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All About Jewels:
Illustrated Dictionary of Jewelry
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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Crystal Systems


Crystals are divided into seven crystal systems, according to their optical properties (how light bends within the crystal), plane of symmetry, axis of symmetry, center of symmetry, crystallographic axis. Within each of the systems, the cyrstals can mineralize into different crystal habits (form). The seven crystal systems are:

System Number of Crystallographic Axes Number of Planes of Symmetry Number of Axes of Symmetry Center of Symmetry Refractivity Shapes Gems
Cubic systems 3 crystallographic axes (of equal length) at right angles to each other 9 13 axes (3 tetragonal, 4 trigonal, 6 digonal) Yes singly refractive cube cube - octahedron diamond, garnet, spinel
Tetragonal systems 3 crystallographic axes at right angles to each other - two of equal length, one longer or shorter 5 5 axes (4 tetragonal, 1 trigonal) Yes doubly refractive tetragron tetragron2 rutile, idocrase, zircon
Hexagonal systems 4 crystallographic axes, three of equal length, intersecting at 60 degree angles, the other three are longer or shorter and perpendicular to the first three 7 7 axes (1 hexagonal, 6 digonal) Yes doubly refractive 6-sided prism terminating in a single face apatite, aquamarine, emerald
Trigonal systems 4 crystallographic axes, three of equal length, intersecting at 60 degree angles, the other three are longer or shorter and perpendicular to the first three 3 4 axes (1 trigonal, 2 digonal) Yes doubly refractive Trigonal quartz, ruby, sapphire, tourmaline
Orthorhombic systems 3 crystallographic axes of different lengths at right angles to each other 3 3 axes (3 digonal) Yes doubly refractive - chrysoberyl, peridot, topaz
Monoclinic systems 3 crystallographic axes of different lengths, 2 at right angles to each other, the third at a different angle 1 1 axis (1 digonal) Yes doubly refractive Monoclinic brazilianite, kunzite, moonstone, jade (nephrite, jadeite), malachite, sphene
Triclinic systems 3 crystallographic axes of different lengths, all at different angles none none Yes doubly refractive - amazonite, axinite, Labradorite, rhodonite, turquoise

All About Jewels:
Illustrated Dictionary of Jewelry
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Click on an underlined word for more information on that subject.
If the jewelry term you are looking for is not in the dictionary, please e-mail me and I'll add it.




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