Silicates are a large family of ceramics. They comprise all clays as well as most rocks and sands. They consist of different arrangements of Si and O atoms, the two most abundant elements in the earth’s crust. They can range from the simplest form of silica, SiO2, to very complex arrangements of silicon atoms and oxygen atoms. Usually each silicon atom is surrounded in a covalently bonded tetrahedron of oxygen atoms. Silica glasses are commonly formed as a non-crystalline solid.