pyroxenegroup

The pyroxene group is a family of inosilicate minerals characterized by single-chain SiO4 tetrahedra that share two oxygen vertices to form [SiO3]n chains. They have a general chemical formula XY(Si,Al)2O6 in which X and Y are metal cations that occupy distinct octahedral sites. Pyroxenes typically exhibit two good cleavage planes at near 90 degrees and occur in a wide range of colors from green to brown to black.

Pyroxenes are divided into two subgroups based on crystal structure: orthopyroxenes, which are orthorhombic, and clinopyroxenes, which are monoclinic. Common orthopyroxenes include enstatite (MgSiO3) and ferrosilite (FeSiO3). Clinopyroxenes include diopside (CaMgSi2O6), hedenbergite (CaFeSi2O6), and the augite group, which often has mixed Ca, Na, Mg, Fe, and Al in the X and Y sites. Jadeite (NaAlSi2O6) is another important clinopyroxene. Pyroxenes exhibit extensive solid solution, with end-members such as enstatite–ferrosilite and diopside–hedenbergite illustrating metal cation substitutions.

Occurrences of pyroxenes are widespread in igneous and metamorphic rocks. They are abundant in mafic and ultramafic rocks such as basalt, gabbro, and peridotite, and in metamorphic rocks like granulites and eclogites. Their compositions and temperatures of stability make them useful for petrological geothermometry and geobarometry, as well as for interpreting rock formation and evolutionary histories.

The name pyroxene derives from Greek roots meaning fire and strange, reflecting historical observations of their appearance and properties.