Aegirine

Aegirine is a mineral. It is a member of the clinopyroxene group of inosilicate minerals. Acmite is a fibrous green-colored variety of aegirine, with the name also used as a synonym. It was first described in 1821, in Kongsberg, Norway.

The name aegirine is derived from Ægir , a Norse mythological figure (god of the sea), as the mineral was first described from Norway.

A synonym for the mineral is acmite (from Greek ἀκμή "point, edge") in reference to the typical pointed crystals.

Aegirine is the sodium endmember of the aegirine–augite series.^{[citation needed]}

It has the chemical formula NaFeSi₂O₆, in which the iron is present as the ion Fe³⁺. In the aegirine–augite series, the sodium is variably replaced by calcium with iron(II) and magnesium replacing the iron(III) to balance the charge. Aluminum also substitutes for the iron(III). Acmite is a fibrous green-colored variety.^{[citation needed]}

Aegirine occurs as dark green monoclinic prismatic crystals. It has a glassy luster and perfect cleavage, "in two directions at near 90 degree angles". It is described on Mindat.org as "slightly resinous", with its colour "dark green to greenish black, reddish brown, [or] black" Its Mohs hardness is 6 and its specific gravity is between 3.5 and 3.6.

Associated minerals include augite, nepheline, andradite, baryte, quartz, spessartine, riebeckite, biotite, sodalite, and albite.

The acmite variety was first described in 1821, at Kongsberg, Norway, and the aegirine variety in 1835 for an occurrence in Rundemyr, Øvre Eiker, Buskerud, Norway.