a polymorph of quartz occurring in the form of small crystals, commonly twinned, in siliceous volcanic rocks.
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How to use tridymite in a sentence
The crystals, called cristobalite and tridymite, swim in clouds around stars just before they begin to form planets.Space Bling: From Diamond Planets to Crystal Oceans to Precious Moon Jewels | Alexa Valiente, Jaewon Kang | October 13, 2012 | THE DAILY BEAST
When crystalline grains or blebs of quartz occur, we have a quartz-trachyte; when tridymite is abundant, as in the trachyte of Co.Volcanoes: Past and Present | Edward Hull
Spherulites may be regarded as radiate aggregates of such microliths (mostly felspar mixed with quartz or tridymite).