Acmite is a member of the clinopyroxene group of inosilicates. Acmite is the sodium endmenber of the acmite-augite series. Acmite has the chemical formula NaFeSi2O6 in which the iron is present as Fe3+. In the acmite-augite series the sodium is variably replaced by calcium with iron(II) and magnesium replacing the iron(III) to balance the charge. Aluminium also substitutes for the iron(III).
Characteristics[edit | edit source]
Acmite occurs as dark green monoclinic prismatic crystals. It has a glassy luster and perfect cleavage. The Mohs hardness varies from 5 to 6 and the specific gravity is 3.2 to 3.4.
Acmite Commonly occurs in alkalic igneous rocks, also in regionally metamorphosed schists, gneisses, and iron formations; in blueschist facies rocks, and from sodium metasomatism in granulites. It may occur as an authigenic mineral in shales and marls.