What is a polymorph in geology?

In geology, polymorphs occur when two compounds of the same composition have different crystalline structures. An example of a polymorph is quartz that is subjected to high temperatures, transforming to trydimite and then crystobalite. Trydimite and crystobalite are considered polymorphs of quartz.

Polymorphs are very common in geology. A popular example of carbon polymorphs are diamond and graphite. Breaking the word polymorph into smaller sections gives away the meaning of the word. "Poly" is a root word meaning many. "Morph" means to undergo a gradual transformation. The word "polymorph" essentially means many transformations, such as carbon being transformed to diamond or graphite.