It was noticed by the ancient Greeks that a certain mineral, quartz, usually occurred in forms having a characteristic shape, being bounded by flat faces. From the transparency of this mineral and the occurrence in it of included material, it was thought quartz resulted from the freezing of water under intense cold, and hence the name krustallos—meaning clear ice—was given to the substance. There were, however, numerous other minerals known to the ancients which occurred in forms bounded by flat faces, and so, by a natural extension of the term, krustallos came to signify any mineral showing such forms. These forms are crystals and their study crystallography.
KeywordsCrystallographic Axis Symmetry Class Unit Form Trigonal Prism Hexagonal Prism
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