Oxides generally are found in Silica-poor rock types. Oxides technically include the Silicates, but are usually refered to separately. Common Oxides Corundum Corundum is found in almost every conceivable color, all called sapphire unless it is red, which is ruby. Corundum is second only to diamond in hardness. This is an uncut crystal from the Gem and Mineral Collection of the Smithsonian's National Museum of Natural History .
Silicates are relatively hard and generally insoluable in acids.
The structure of the all silicates is based on the silica tetrahedron, composed of 1 Silicon cation surrounded by 4 Oxygen anions. This page was brought to you by Philip Ryland . Please email any suggestions or comments. There have been visits to this page since July 22, 1995.