Aegirine

Aegirine (dark) with minor feldspar (light) from Malawi

General
Category| Silicate mineral, pyroxene
Formula
(repeating unit)| NaFe3+[Si

Strunz classification| 9.DA.25
Crystal system| Monoclinic
Crystal class| Prismatic (2/m)
(same H-M symbol)
Space group| C2/c
Unit cell| a = 9.658, b = 8.795
c = 5.294 [Å], β = 107.42°; Z = 4
Identification
Formula mass| 231.00 g/mol
Color| Dark Green, Greenish Black
Crystal habit| Prismatic crystals may be in sprays of acicular crystals, fibrous, in radial concretions
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
|re|er}}| 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 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.

## Contents

* 1 Etymology
* 2 Chemistry and description
* 3 Occurrence
* 4 Uses
* 5 See also
* 6 References
* 7 External links

## Etymology

The name aegirine is derived from Ægir, a Norse mythological figure (god of the sea), as the mineral was first described from Norway.[1][2]

A synonym for the mineral is acmite (from Greek ἀκμή "point, edge") in reference to the typical pointed crystals.Cite error: Invalid `<ref>` tag; refs with no name must have content

## Chemistry and description

Syenite with aegirine and acmite from Magnet Cove, Arkansas, US

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.[2] It has a glassy luster and perfect cleavage, "in two directions at near 90 degree angles".[6] 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.[2][3]

Associated minerals include augite, nepheline, andradite, baryte, quartz, spessartine, riebeckite, biotite, sodalite, and albite.[6]

## Occurrence

The acmite variety was first described in 1821, at Kongsberg, Norway,[7] and the aegirine variety in 1835 for an occurrence in Rundemyr, Øvre Eiker, Buskerud, Norway.[2]

This mineral commonly occurs in alkalic igneous rocks, nepheline syenites, carbonatites, and pegmatites. It also appears 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]

Major localities include Mont Saint-Hilaire, Quebec, Canada; Kongsberg, Norway; Narsarssuk, Greenland; Kola Peninsula, Russia; Magnet Cove, Arkansas, US; Kenya; Scotland, and Nigeria.[6]

Aegirine also occurs in the syenite at the Bowral quarries in New South Wales, Australia, as described in a 1906 paper by geologist and later Antarctic explorer Douglas Mawson.[8][9]

## Uses

Aegirine is sometimes used as a gemstone.[10]

## See also

* List of minerals

## References

1. ↑ 1.0 1.1 1.2 "Aegirine". Handbook of Mineralogy (version 1.2 ed.). Mineral Data Publishing. 2001. https://rruff.geo.arizona.edu/doclib/hom/aegirine.pdf.
2. ↑ 2.0 2.1 2.2 2.3 2.4 "Aegirine". https://www.mindat.org/min-31.html.
3. ↑ 3.0 3.1 "Aegirine Mineral Data". https://webmineral.com/data/Aegirine.shtml.
4. ↑ Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7 (via Internet Archive
5. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
6. ↑ 6.0 6.1 6.2 "AEGIRINE (Sodium Iron Silicate)". http://mineral.galleries.com/minerals/silicate/aegirine/aegirine.htm.
7. ↑ Dana, James Dwight (1855). Manual of Mineralogy (7th ed.). Philadelphia, PA: Durrie & Peck.
8. ↑ Jago, James B.; Pharaoh, Mark D. (2 January 2016). "Pre-Antarctic Mawson in South Australia and western New South Wales". Transactions of the Royal Society of South Australia (Informa UK) 140 (1): 107–128. doi:10.1080/03721426.2016.1149323. ISSN 0372-1426. Bibcode: 2016TRSAu.140..107J. https://www.researchgate.net/publication/297672396.
9. ↑ "The Minerals and Genesis of the Veins and Schlieren Traversing the Aegirine-Syenite in the Bowral Quarries". Proc. Linn. Soc. N.S.W., 381, pp. 580-607.
10. ↑ Manutchehr-Danai, Mohsen (9 March 2013). Dictionary of Gems and Gemology. Springer Science & Business Media. p. 5. ISBN 978-3-662-04288-5. https://books.google.com/books?id=2UX1CAAAQBAJ.

## External links

* Mineral Galleries

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