pyroxene An important group of inosilicates (chain silicates) comprising the orthorhombic pyroxenes (orthopyroxenes) and the monoclinic pyroxenes (clinopyroxenes) with the general formula XYZ₂O₆, where × = Mg, Fe, Ca, or Na; Y = Mg, Fe, Fe³⁺, or Al; and Z = Si (and some Al substitution). The main orthopyroxenes are enstatite and orthoferrosilite; the main clinopyroxenes include diopside, hedenbergite, augite, pigeonite, and jadeite, and also the alkali pyroxenes aegirine and aegirine augite (note that wollastonite, although similar to the pyroxenes, has a different atomic structure); sp. gr. 3.0–3.5; hardness 5–6; colours variable, but usually dark greens, browns, or black; vitreous lustre; crystals usually short or columnar prisms; well-marked cleavage; widely distributed in both igneous and metamorphic rocks.

py·rox·ene / pīˈräkˌsēn; pə-/ • n. any of a large class of rock-forming silicate minerals, generally containing calcium, magnesium, and iron and typically occurring as prismatic crystals.

pyroxene Group of rock-forming, silicate minerals, usually coloured dark green, brown, and black. Crystals are usually short prisms with good cleavages. Hardness 2.3–4; r.d. 5.5–6.