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
source: WordNet 3.0
Silicon dioxide, SiO&?;. It constitutes ordinary quartz (also opal and tridymite), and is artifically prepared as a very fine, white, tasteless, inodorous powder.
