Changes

'''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>

'''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: