silicate, chemical compound containing silicon, oxygen, and one or more metals, e.g., aluminum, barium, beryllium, calcium, iron, magnesium, manganese, potassium, sodium, or zirconium. Silicates may be considered chemically as salts of the various silicic acids. For a long time classified as ortho-, meta-, di-, or trisilicates according to the acid from which they are (theoretically) derived, they are now also classified by an X-ray diffraction method according to their crystalline structure. Silicates are widely distributed in nature, making up most of the earth's outer crust. Most of the common rock-forming minerals (e.g., quartz, feldspar, mica, and pyroxene) are silicates, as are asbestos, beryl, aquamarine, emerald, serpentine, and talc. Clay consists essentially of hydrous aluminum silicates mixed with other substances. Glass is a mixture of silicates, as is water glass. See sodium silicate.