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aegirine 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; and CLINOPYROXENE.