Pyroxene mineral, NaFe³⁺Si₂O₆; sp. gr. 3.5; hardness 6; monoclinic; greenish-black or brown; occurs as fairly short, prismatic crystals in igneous and metamorphic rocks. A variety intermediate in composition between aegirine and augite is called ‘aegirine–augite’. See also augite; clinopyroxene.