pyroxenitic

Pyroxenitic is an adjective used in geology to describe rocks whose mineralogical assemblage is dominated by pyroxene. In practice, pyroxenitic rocks are ultramafic to mafic and are characterized by a primary presence of pyroxene minerals—chiefly clinopyroxene (augite, diopside) and orthopyroxene (enstatite, ferrosilite)—with little or no plagioclase feldspar. Olivine may be present as an accessory phase, and minor minerals such as magnetite, chromite, amphibole, or hornblende may occur.

Pyroxenites are typically granular or massive, and they can form as cumulate rocks in mafic-ultramafic intrusions or as mantle-derived xenoliths carried by basalts. They occur in ophiolites and in regions where mantle residues have become pyroxene-rich, often alongside or interlayered with peridotites, dunites, and other ultramafic lithologies. Textures may range from coarse-grained to cumulate-like with intergrowths of pyroxenes.

Geochemically, pyroxenites may represent crystallization residues of basaltic magmas with high pyroxene saturation or metasomatic products of mantle domains enriched in pyroxene. They are distinct from peridotites, which are olivine-rich, and from gabbros, which include substantial feldspar. The term pyroxenitic is therefore used to describe rocks whose defining feature is a pyroxene-dominated mineralogy, whether the rocks are mantle-derived xenoliths or igneous intrusions.