Definition of tridymite
: 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)
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Origin and Etymology of tridymite
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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