Silicates

Silicates are the largest and most common class of minerals on Earth, composed primarily of silicon and oxygen, with various metals often present. Their defining feature is the silicon-oxygen tetrahedron (SiO4) in which a silicon atom is bonded to four oxygen atoms. These tetrahedra link by sharing oxygen corners to form structures that range from isolated units to three-dimensional frameworks. The degree of polymerization among the tetrahedra governs silicate classification and properties.

The main structural groups are nesosilicates (orthosilicates) with isolated SiO4 tetrahedra; sorosilicates containing pairs of tetrahedra sharing one oxygen (Si2O7); cyclosilicates consisting of rings of linked tetrahedra (such as Si3O9 or Si6O18 units); inosilicates including single-chain silicates (pyroxenes) with repeating SiO3 units and double-chain silicates (amphiboles) with Si4O11 units; phyllosilicates forming two-dimensional sheets (Si2O5) such as micas and clays; and tectosilicates with a three-dimensional framework in which all oxygens are shared, exemplified by quartz and the feldspars.

Silicate minerals occur across all rock types and geological environments, forming through magmatic crystallization, metamorphism, or sedimentary diagenesis. Their physical properties, such as hardness, cleavage, and stability, are strongly influenced by the connectivity of the SiO4 tetrahedra. Economically and technologically, silicates are central to construction materials (cement, glass sands), ceramics, and numerous industrial minerals. Their abundance and versatility underpin their dominant role in Earth's crust and mantle.