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 cleavage angles. The general formula is X1–pY1+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.
Subjects: Earth Sciences and Geography — Chemistry.