Aegirine

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Aegirine

Aegirine crystals in matrix
General
Category Mineral
Chemical formula NaFe3+[ Si2O6]
Identification
Molecular Weight 231.00
Color Dark Green, Greenish Black
Crystal habit acircular
Crystal system Monoclinic
Cleavage Distinct/good
Fracture brittle
Mohs Scale hardness 6
Luster Vitrious
Refractive index biaxial
Birefringence 0.037 - 0.061
Dispersion r > v
Streak Yellowish-grey
Specific gravity 3.52
Diaphaneity subtransparent to translucent to opaque

Aegirine is an inosilicate member of the clinopyroxene group. Aegirine is the sodium endmenber of the aegirine-augite series. Aegirine has the chemical formula NaFeSi2O6 in which the iron is present as 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. Aluminium also substitutes for the iron(III). It is also known as acmite.

Aegirine occurs as dark green monoclinic prismatic crystals. It has a glassy lustre and perfect cleavage. The Mohs hardness varies from 5 to 6 and the specific gravity is 3.2 to 3.4.

Aegirine
Aegirine

It occurs in alkali nepheline syenites and similar igneous rocks. Localities include Mont Saint-Hilaire, Quebec, Canada; Kongsberg, Norway; Narsarssuk, Greenland; Kola Peninsula, Russia; Magnet Cove, Arkansas, USA; Kenya; Scotland and Nigeria.

Aegirine was named after Ægir, the Teutonic god of the sea. A synonym for the mineral is acmite (from Greek) in reference to the typical pointed crystals.

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