silica -
a white or colorless vitreous insoluble solid (SiO2); various forms occur widely in the earth's crust as quartz or cristobalite or tridymite or lechatelierite
oxide any compound of oxygen with another element or a radical
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
cristobalite a white mineral consisting of silica; found in volcanic rocks
