orthopyroxenebearing

Orthopyroxenebearing refers to rocks or mineral assemblages in which orthopyroxene is a major or notable phase. Orthopyroxene is a group of inosilicate minerals in the pyroxene family with the general composition (Mg,Fe)SiO3, forming a solid-solution series between enstatite (MgSiO3) and ferrosilite (FeSiO3). The orthorhombic pyroxenes are distinct from clinopyroxenes (monoclinic) in crystal symmetry and some optical properties.

Occurrence and formation: Orthopyroxene-bearing rocks are common in mafic and ultramafic settings. In igneous rocks, orthopyroxene occurs in peridotites, pyroxenites, gabbros, norites, and basalts, often alongside olivine and plagioclase. In metamorphic rocks, orthopyroxene forms under high-temperature conditions and is typical of granulites, some high-grade metabasites, and related rocks, reflecting a high-temperature, potentially high-pressure history.

Diagnostic features: In hand specimen, orthopyroxene can appear as elongated, prismatic crystals. In thin section, it exhibits characteristic cleavage and optical properties that help distinguish it from clinopyroxene, which has different symmetry and diagnostic refractive features. Identification relies on mineral chemistry (Mg–Fe content) and crystallography.

Geologic significance: The presence of orthopyroxene provides petrogenetic and metamorphic constraints, informing crystallization sequences, partial melting histories, and crustal or mantle conditions. Orthopyroxene-bearing assemblages are used in geothermobarometry to estimate temperature and pressure during rock formation and metamorphism.