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tridymite

[trid-uh-mahyt] /ˈtrɪd əˌmaɪt/
noun, Mineralogy
1.
a polymorph of quartz occurring in the form of small crystals, commonly twinned, in siliceous volcanic rocks.
Origin
1865-1870
1865-70; < German Tridymit, equivalent to tridym- (Greek trídym(os) triple, equivalent to tri- tri- + ()dymos didymous) + -it -ite1
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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Examples from the web for tridymite
  • Only six forms appear on this diagram, and there is considerable question whether tridymite is truly stable.
  • Cristobalite and tridymite are two other forms of crystalline silica.
  • Other types of silica include cristobalite and tridymite.
Encyclopedia Article for tridymite

silica 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)

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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