Silicate

A silicate is a chemical compound containing silicon and oxygen, usually with metal cations. The silicon–oxygen tetrahedron, SiO4, is the fundamental building block. In silicates, tetrahedra link by sharing oxygen atoms to form structures with varying degrees of polymerization. Silicate minerals are classified by this polymerization into several groups: nesosilicates (isolated tetrahedra); sorosilicates (paired tetrahedra, Si2O7); cyclosilicates (ring structures, such as Si6O18 in certain minerals); inosilicates (single chains in pyroxenes and double chains in amphiboles); phyllosilicates (sheets, as in micas and clays); and tectosilicates (three-dimensional frameworks, as in quartz and feldspars).

Common silicate classes with representative minerals include: nesosilicates such as olivine; cyclosilicates such as beryl; inosilicates such as pyroxenes and amphiboles; phyllosilicates such as muscovite, illite, and kaolinite; and tectosilicates such as quartz and feldspars. The dominant cations—sodium, potassium, calcium, magnesium, iron, and aluminum—balance charge and influence crystal structure and properties. Silicates are the most abundant mineral group in Earth’s crust and play a central role in geology, petrology, and industry.

Occurrence and uses: silicate minerals form by crystallization from silicate melts, metamorphism, and weathering, and are found in igneous, metamorphic, and sedimentary rocks, as well as soils and sands. Industrially important silicates include quartz for glass and electronics, feldspars for ceramics and glass, and various clays and layered silicates used in ceramics, economics, and industry.