Inosilicates

Inosilicates are a class of silicate minerals characterized by silicon-oxygen tetrahedra linked into one-dimensional chains. In this structural arrangement, tetrahedra share two of their oxygens with neighboring tetrahedra, producing repeating units that extend along a chain. This chain polymerization differentiates inosilicates from other silicate groups such as nesosilicates (isolated tetrahedra) and framework or sheet silicates.

The major subgroups of inosilicates are single-chain inosilicates, or pyroxenes, and double-chain inosilicates, or amphiboles. Pyroxenes form in single chains and typically occur in igneous and metamorphic rocks. Common examples include enstatite (MgSiO3), diopside (CaMgSi2O6), and augite (a calcium-magnesium-iron silicate). Pyroxenes generally exhibit two cleavage directions at about 90 degrees and occur in monoclinic or orthorhombic crystal systems. Amphiboles consist of double chains and are often found in hydrated igneous and metamorphic rocks. Notable members include hornblende and tremolite-actinolite groups; amphiboles typically show two cleavage directions at approximately 60 and 120 degrees and belong to monoclinic or orthorhombic systems.

Inosilicates are important indicators in geology because their composition and structure reflect the conditions of rock formation and metamorphism. They exhibit extensive solid-solution series, such as the enstatite–forsterite and diopside–hedenbergite series in pyroxenes, and various substitutions within amphibole groups. Their presence helps characterize rock types, temperature, pressure, and hydration history in igneous and metamorphic environments.