High Quality Content by WIKIPEDIA articles! Tridymite is a high-temperature polymorph of quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal triclinic crystals, or scales, in cavities in acidic volcanic rocks. Its chemical formula is SiO2. Tridymite was first described in 1868 and the type location is in Hidalgo, Mexico. The name is from the Greek Tridymos for triplet as tridymite commonly occurs as twinned crystal trillings. Tridymite can occur in several crystalline forms, which are metastable at ambient conditions, the most common being ? and ?. Alpha phase is orthorhombic, Pearson symbol oS24, group C2221, No.20 whereas ?-tridymite is hexagonal, hP12, P63/mmc, No. 194. ?-tridymite converts to ?-cristobalite at 1470 °C. Данное издание представляет собой компиляцию сведений, находящихся в свободном доступе в среде Интернет в целом, и в информационном сетевом ресурсе "Википедия" в частности. Собранная по частотным запросам указанной тематики, данная...