tridymite

tridymite
/trid"euh muyt'/, n. Mineral.
a polymorph of quartz occurring in the form of small crystals, commonly twinned, in siliceous volcanic rocks.
[1865-70; < G Tridymit, equiv. to tridym- (Gk trídym(os) triple, equiv. to tri- TRI- + (dí)dymos DIDYMOUS) + -it -ITE1]

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       Properties of selected silica mineralssilica mineral, the stable form of silica (silicon dioxide, SiO2) at temperatures between 870° and 1,470° C (1,598° and 2,678° F); at lower temperatures it transforms to high-quartz, at higher to cristobalite. It has three modifications: high-tridymite, middle-tridymite, and low-tridymite. Tridymite forms thin hexagonal plates that are generally twinned, often in groups of three; its name alludes to this habit. It commonly occurs in igneous rocks, more abundantly than cristobalite, as in the trachytes of Rhineland-Palatinate, Germany; northern Italy; and in the Massif Central, France. Tridymite, also found in meteorites, has the same chemical composition as coesite, cristobalite, stishovite, lechatelierite, and quartz but has a different crystal structure. For detailed physical properties, see silica mineral (Table 2 (Properties of selected silica minerals)).

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  • tridymite — trid·y·mite …   English syllables

  • tridymite — n. a crystallized form of silica, occurring in cavities of volcanic rocks. Etymology: G Tridymit f. Gk tridumos threefold (as TRI , didumos twin), from its occurrence in groups of three crystals …   Useful english dictionary

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