silicon dioxide - a white or colorless vitreous insoluble solid (SiO2); various forms occur widely in the earth's crust as quartz or cristobalite or tridymite or lechartelieritecristobalite - a white mineral consisting of silica; found in volcanic rocks lechartelierite - a mineral form of vitreous or glassy silica; formed by the melting of quartz sand (as by lightning or a meteorite) quartz - a hard glossy mineral consisting of silicon dioxide in crystal form; present in most rocks (especially sandstone and granite); yellow sand is quartz with iron oxide impurities chert - variety of silica containing microcrystalline quartz flint - a hard kind of stone; a form of silica more opaque than chalcedony oxide - any compound of oxygen with another element or a radical silex - a pure form of finely ground silica |