In chemistry, a silicate is a compound consisting of silicon and oxygen (SixOy), one or more metals, and possibly hydrogen. It is also used to denote the salts of silica or of one of the silicic acids.
Silicate minerals are noted for their tetrahedral form. Sometimes the tetrahedra are joined in chains, double chains, sheets, and three-dimensional frameworks. They are subclassified into groups based on the degree of polymerization of the tetrahedra, such as nesosilicates, cyclosilicates, and so forth.
In geology and astronomy, the term silicate is used to denote a type of rock that consists of silicon and oxygen (usually as SiO2 or SiO4), one or more metals, and possibly hydrogen. Such rocks range from granite to gabbro. Most of the Earth's crust is made up of silicate rocks, as are the crusts of other terrestrial planets.
Geologically, silicate minerals are divided according to their molecular structure into the following groups:
- Olivine (single tetrahedron)
- Pyroxene (single chain)
- Amphibole (double chain)
- Micas and clays (sheet)
- Feldspars (framework)
- Quartz (SiO2 framework)