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TRIDYMITE

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Originally appearing in Volume V27, Page 268 of the 1911 Encyclopedia Britannica.
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TRIDYMITE , a See also:

mineral consisting of See also:silicon See also:oxide or See also:silica, SiO2, but differing from See also:quartz in crystalline See also:form. The crystals are small, thin hexagonal plates or scales, which are usually twinned together in See also:groups of three; hence the name of the mineral, from See also:Greek rplSvilos, triplet. The apparent hexagonal plates are themselves pseudo-symmetric twins of optically biaxial material, and the exact crystalline form is doubtful. The plates are colourless and transparent and have a vitreous lustre. The hardness is 7 and the specific gravity 2.3 (that of quartz being 2.65). Unlike quartz, it is soluble in a boiling See also:solution of See also:sodium carbonate. Tridymite occurs in the cavities of See also:acid volcanic rocks (See also:rhyolite, See also:trachyte and See also:andesite); the best-known localities are Cerro See also:San Cristobal near See also:Pachuca in See also:Mexico, the Euganean Hills near See also:Padua, and the See also:Siebengebirge on the See also:Rhine. Probably identical with tridymite is the form of silica known as asmanite, found in the See also:meteorite which See also:fell at Breitenbach in the See also:Erzgebirge, Bohemia. (L. J.

End of Article: TRIDYMITE

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