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expand and merge from Crystal Systems
'''Crystal systems''' are a way of characterising the 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:
*[[Hexagonal system|Hexagonal]], requires 1 sixfold axis of rotation.
*[[Isometric system|Isometric or cubic]], requires 4 threefold axes of rotation.
*[[Monoclinic system|Monoclinic]], requires either 1 twofold axis of rotation or 1 mirror plane.
*[[Orthorhombic system|Orthorhombic]], requires either 3 twofold axes of rotation or 1 twofold axis of rotation and two mirror planes.
*[[Trigonal system|Trigonal or rhombohedral]], requires 1 threefold axis of rotation.
*[[Tetragonal system|Tetragonal]], requires 1 fourfold axis of rotation.
*[[Triclinic system|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==
<references/>
[[Category:Crystallography]]
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:
*[[Hexagonal system|Hexagonal]], requires 1 sixfold axis of rotation.
*[[Isometric system|Isometric or cubic]], requires 4 threefold axes of rotation.
*[[Monoclinic system|Monoclinic]], requires either 1 twofold axis of rotation or 1 mirror plane.
*[[Orthorhombic system|Orthorhombic]], requires either 3 twofold axes of rotation or 1 twofold axis of rotation and two mirror planes.
*[[Trigonal system|Trigonal or rhombohedral]], requires 1 threefold axis of rotation.
*[[Tetragonal system|Tetragonal]], requires 1 fourfold axis of rotation.
*[[Triclinic system|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==
<references/>
[[Category:Crystallography]]