noun Mineralogy.
  1. a polymorph of quartz occurring in the form of small crystals, commonly twinned, in siliceous volcanic rocks.

Origin of tridymite

1865–70; < German Tridymit, equivalent to tridym- (Greek trídym(os) triple, equivalent to tri- tri- + (dí)dymos didymous) + -it -ite1 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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Contemporary Examples of tridymite

Historical Examples of tridymite