Silicates are compounds of silicon, oxygen and other elements. Silica (silicon dioxide), silicate, and aluminosilicate minerals make up over 90% of the Earth's crust. Naturally occurring silicates are important building materials and make up the clays upon which ceramics and brickmaking are based. Silica is the basis of glass technology, and synthetic silicates are important in detergent and adhesive applications.

Like carbon, the silicon atom has a marked tendency to form four covalent bonds. Unlike carbon, however, it has little or no tendency to form multiple bonds. In silica, each silicon atom is bonded to four oxygen atoms and each oxygen atom is bonded to two silicons (Figure 1). Energetic considerations prohibit two silicon atoms from sharing more than one bonding oxygen. One can visualize the structures of silica by thinking of the SiO₄ units as tetrahedra sharing corners. A little experimentation with models reveals that numerous different silica structures...