- Aegirine
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Aegirine 
Aegirine crystals in matrixGeneral Category Silicate mineral, Pyroxene Chemical formula NaFe3+[ Si2O6] Crystal symmetry Monoclinic 2/m Unit cell a = 9.658 Å, b = 8.795 Å, c = 5.294 Å, β = 107.42°; Z=4 Identification Molar mass 231.00 Color Dark Green, Greenish Black Crystal habit Prismatic crystals may be in sprays of acicular crystals, fibrous, in radial concretions Crystal system Monoclinic Prismatic Twinning Simple and lamellar twinning common on {100} Cleavage Good on {110}, (110) ^ (110) ≈87°; parting on {100} Fracture Uneven Tenacity Brittle Mohs scale hardness 6 Luster Vitreous to slightly resinous Streak Yellowish-grey Diaphaneity Translucent to opaque Specific gravity 3.50 - 3.60 Optical properties Biaxial (-) Refractive index nα = 1.720 - 1.778 nβ = 1.740 - 1.819 nγ = 1.757 - 1.839 Birefringence δ = 0.037 - 0.061 Pleochroism X = emerald green, deep green; Y = grass-green, deep green, yellow; Z = brownish green, green, yellowish brown, yellow 2V angle Measured: 60° to 90°, Calculated: 68° to 84° Dispersion moderate to strong r > v References [1][2][3][4] Aegirine is a member of the clinopyroxene group of inosilicates. Aegirine is the sodium endmember 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, which is a fibrous, green-colored variety.
Aegirine 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.
Aegirine
Commonly occurs in alkalic igneous rocks, nepheline syenites, carbonatites and pegmatites. 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. It occurs in association with potassic feldspar, nepheline, riebeckite, arfvedsonite, aenigmatite, astrophyllite, catapleiite, eudialyte, serandite and apophyllite.[1]
Localities include Mont Saint-Hilaire, Quebec, Canada; Kongsberg, Norway; Narsarssuk, Greenland; Kola Peninsula, Russia; Magnet Cove, Arkansas, USA; Kenya; Scotland and Nigeria.
It was first described in 1835 for an occurrence in Rundemyr, Øvre Eiker, Buskerud, Norway. Aegirine was named after Ægir, the Teutonic god of the sea.[2] A synonym for the mineral is acmite (from Greek ἀκμή "point, edge") in reference to the typical pointed crystals.
References
- ^ a b http://rruff.geo.arizona.edu/doclib/hom/aegirine.pdf Handbook of Mineralogy
- ^ a b http://www.mindat.org/min-31.html Mindat
- ^ http://webmineral.com/data/Aegirine.shtml Webmineral
- ^ Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7
Categories:- Inosilicates
- Sodium minerals
- Iron minerals
- Pyroxene group
- Monoclinic minerals
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