pyroxene

pyroxene , name given to members of a group of widely distributed rock minerals called metasilicates in which magnesium, iron, and calcium, often with aluminum, sodium, lithium, manganese, or zinc occur as X in the chemical formula XSiO ₃ . The pyroxene minerals crystallize in three different systems—orthorhombic, monoclinic, and triclinic—but all have a fundamental prism with angles of 87° to 93° and cleavages parallel to the prism angles. They are commonly white, grayish white, greenish white, greenish black, black, or brown, but other varieties occur. Pyroxene minerals are found chiefly in igneous and metamorphic rocks and in lunar rocks. Varieties include enstatite, bronzite, hypersthene, diopside, wollastonite, augite, pectolite, spodumene, and rhodonite.

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.