A group of ferromagnesian rock-forming silicate minerals. They are common in basic igneous rocks but may also be developed by metamorphic processes in gneisses, schists, and marbles. Pyroxenes have a complex crystal chemistry; they are composed of continuous chains of silicon and oxygen atoms linked by a variety of other elements. They are related to the amphiboles, from which they differ in having single rather than double chains. The chain structures of pyroxenes are simple, although there exist other single-chain silicate minerals with more complex structures. The general formula is X_1–pY_1+pZ₂O₆, where X = Ca,Na; Y = Mg,Fe²⁺,Mn,Li,Al,Fe³⁺,Ti; and Z = Si,Al.

Orthorhombic pyroxenes (orthopyroxenes), (Mg,Fe)₂Si₂O₆, vary in composition between the end-members enstatite (Mg₂Si₂O₆) and orthoferrosilite (Fe₂Si₂O₆). Monoclinic pyroxenes (clinopyroxenes), the larger group, include:

diopside, CaMgSi₂O₆; hedenbergite, CaFe²⁺Si₂O₆; johannsenite, CaMnSi₂O₆; augite, (Ca,Mg,Fe,Ti,Al)₂(Si,Al)₂O₆; aegirine, NaFe³⁺Si₂O₆; jadeite (see jade); pigeonite (Mg,Fe²⁺,Ca)(Mg,Fe²⁺)Si₂O₆.