Silicaat

Silicaat, or silicate, is a broad class of minerals and chemical compounds whose structure is based on silicon-oxygen tetrahedra (SiO4). In silicates, the tetrahedra share oxygen atoms to form isolated units, chains, sheets, rings, or three-dimensional frameworks. The arrangement of the tetrahedra and the presence of metal cations such as aluminum, iron, or magnesium determine the mineral’s crystal structure and physical properties. Silicate minerals constitute the majority of Earth’s crust, forming the vast majority of rock-forming minerals.

Classification of silicates is based on how the SiO4 tetrahedra connect. Nesosilicates (isolated tetrahedra) include olivine and garnet. Sorosilicates (paired tetrahedra) include epidote group minerals. Cyclosilicates (ring silicates) include minerals such as beryl and tourmaline. Inosilicates consist of single chains (pyroxenes) or double chains (amphiboles). Phyllosilicates form sheet structures, encompassing micas, clays, and talc. Tectosilicates (framework silicates) include the feldspars and quartz, which form three-dimensional networks.

Formation and occurrence: Silicates crystallize from magmatic melts and high-temperature metamorphic fluids, or form and weather into secondary minerals during diagenesis and metamorphism. They are ubiquitous in igneous, metamorphic, and sedimentary rocks, and their stability ranges drive much of mineralogy and tectonics.

Uses and significance: Silicates underpin many industrial materials. Silica (SiO2) and feldspars are central to glass and ceramic production; feldspars and calcium silicates are important in cement and construction materials; clays and phyllosilicates serve as important industrial and natural materials, including pigments, fillers, and adsorbents.