tridymite

noun

trid·​y·​mite

ˈtridəˌmīt

plural -s

: a mineral SiO₂ that is a silica, differs from quartz in its usually minute thin tabular orthorhombic forms of crystallization, and is found in cavities in trachyte and similar rocks (hardness 7, specific gravity 2.28–2.33)

Word History

Etymology

German tridymit, from Greek tridymos threefold (irregular from tri- three + didymos twin) + German -it -ite; from its common occurrence in trillings

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