Dioxide of silicon (SiO2), which appeared in five crystalline polymorphous such as quartz (alpha and beta), tridymite, cristobalite, coesite, and stichovite, in cryptocrystalline such as chalcedony and chert, and in amorphous such as opal (a hydrated silica) and lechatelierite. It is an essential constituent of silicate group of rock forming minerals. It occurs in sand, diatomite, tripoli, flint, chert, etc. Important minerals yield as several gem varieties. Also it is basis form of most glasses and used as an abrasive, to ceramic, etc.
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