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Definition of polymorph

A chemical compound which crystallises in a different crystal class to another compound of identical chemical composition; e.g.: (1) kyanite, andalusite, and sillimanite; (2) quartz, tridymite, cristobalite, coesite, and stishovite. See aso polymorphism.

Allotropy refers specif. to chemical elements crystallizing in more than one class; e.g., graphite, diamond, chaoite, and lonsdaleite. Polymorphism limited to two or three crystal classes is dimorphism or trimorphism, respectively. Individual species are polymorphs (dimorphs, trimorphs). Polytypism refers to variable stacking of identical layer structures in different crystal classes, forming polytypes, normally not considered to be separate species. Polysyngony is where polymorph only vary in unit cell angles, eg. Alpha and beta quartz.

Adj: polymorphic (dimorphic, trimorphic). Adv: polymorphous (dimorphous, trimorphous).

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