Inosilikaatit

Inosilicates are silicate minerals characterized by silicon-oxygen tetrahedra that share oxygens to form chains. The chains occur in two main forms: single chains in pyroxenes and double chains in amphiboles. This structural arrangement leads to distinct physical properties and mineral associations in rocks.

Single-chain inosilicates, or pyroxenes, consist of SiO4 tetrahedra that share two oxygens with neighboring tetrahedra, producing infinite SiO3 chains. The chains are balanced by metal cations occupying octahedral or other sites, giving a general formula such as XY(SiO3)2 for many pyroxenes. Common examples include enstatite (MgSiO3) and diopside (CaMgSi2O6). Pyroxenes typically crystallize in monoclinic or orthorhombic systems and exhibit two cleavages at approximately 90 degrees.

Double-chain inosilicates, or amphiboles, are formed when two single chains are staggered and linked to create double chains with repeating Si8O22(OH)2 units. Their chemistry allows extensive cation substitution in several structural sites, often written in a generalized form as A0-4B2C5Si8O22(OH)2. Amphiboles include hornblende, tremolite, and actinolite. They commonly contain hydroxyl groups and show two cleavage directions at about 56 and 124 degrees.

In geology, inosilicates are widespread in both igneous and metamorphic rocks. Pyroxenes are prevalent in mafic and ultramafic rocks, while amphiboles are abundant in metamorphic rocks such as schists and amphibolites and in certain igneous settings. Their chain structures influence physical properties and are useful indicators of pressure–temperature history in rock-forming environments.

Compared with other silicate classes, inosilicates form chains rather than isolated tetrahedra, rings, sheets, or three-dimensional frameworks, distinguishing them within the silicate mineral family.

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