Difference between revisions of "Crystal system"
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| − | '''Crystal systems''' are a way of characterising | + | '''Crystal systems''' are a way of characterising the three-dimensional shape shape of mineral crystals by their symmetry and thus aiding in their classification. Mineral crystals come in a seemingly infinite range of shapes. But behind this tremendous diversity of form there is a strict order, because crystals always grow according to simple mathematical laws.<ref>Chesterman, Charles W. ''The Audubon Society Field Guide to North American Rocks and Minerals'', Alfred A. Knopf: New York (1987) ''p. 33''</ref> |
There are 6 (or 7)<ref>U.S. classification usually put [[trigonal system|trigonal]] as a sub-set of the [[hexagonal system]], whereas, British practice is to make it a separate class.</ref> crystal systems: | There are 6 (or 7)<ref>U.S. classification usually put [[trigonal system|trigonal]] as a sub-set of the [[hexagonal system]], whereas, British practice is to make it a separate class.</ref> crystal systems: | ||
Revision as of 14:46, July 15, 2016
Crystal systems are a way of characterising the three-dimensional shape shape of mineral crystals by their symmetry and thus aiding in their classification. Mineral crystals come in a seemingly infinite range of shapes. But behind this tremendous diversity of form there is a strict order, because crystals always grow according to simple mathematical laws.[1]
There are 6 (or 7)[2] crystal systems:
- Hexagonal, requires 1 sixfold axis of rotation.
- Isometric or cubic, requires 4 threefold axes of rotation.
- Monoclinic, requires either 1 twofold axis of rotation or 1 mirror plane.
- Orthorhombic, requires either 3 twofold axes of rotation or 1 twofold axis of rotation and two mirror planes.
- Trigonal or rhombohedral, requires 1 threefold axis of rotation.
- Tetragonal, requires 1 fourfold axis of rotation.
- Triclinic, all cases not satisfying the requirements of any other system; thus there is no other symmetry than translational symmetry, or the only extra kind is inversion.
Notes & References
- ↑ Chesterman, Charles W. The Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf: New York (1987) p. 33
- ↑ U.S. classification usually put trigonal as a sub-set of the hexagonal system, whereas, British practice is to make it a separate class.