{{Short description|Member of the clinopyroxene group of inosilicate minerals}} {{use dmy dates|date=August 2025}} {{Infobox mineral | name = Aegirine | category = Silicate mineral, pyroxene | image = Aegirine - Mt Malosa, Zomba, Malawi (alt).jpg | caption = Aegirine (dark) with minor feldspar (light) from Malawi | formula = {{chem2|NaFe(3+)[Si2O6]}} |IMAsymbol=Aeg<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | molweight = 231.00 g/mol | strunz = 9.DA.25 | system = Monoclinic | class = Prismatic (2/m) <br/><small>(same H-M symbol)</small> | symmetry = ''C2/c'' | unit cell = a = 9.658, b = 8.795 <br/>c = 5.294&nbsp;[Å], β = 107.42°; Z&nbsp;=&nbsp;4 | color = Dark Green, Greenish Black | 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) ^ (1{{overline|1}}0) ≈87°; parting on {100} | fracture = Uneven | tenacity = Brittle | mohs = 6 | luster = Vitreous to slightly resinous | polish = | refractive = n<sub>α</sub> = 1.720 – 1.778 n<sub>β</sub> = 1.740 – 1.819 n<sub>γ</sub> = 1.757 – 1.839 | opticalprop = Biaxial (−) | birefringence = δ = 0.037 – 0.061 | dispersion = moderate to strong r > v | pleochroism = X = emerald green, deep green; Y = grass-green, deep green, yellow; Z = brownish green, green, yellowish brown, yellow | fluorescence= | absorption = | 2V = Measured: 60° to 90°, Calculated: 68° to 84° | streak = Yellowish-grey | gravity = 3.50–3.60 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Translucent to opaque | other = | references = <ref name=Handbook>{{cite book|url=https://rruff.geo.arizona.edu/doclib/hom/aegirine.pdf|title= Handbook of Mineralogy| edition= version 1.2| chapter=Aegirine| date=2001 |publisher= Mineral Data Publishing}}</ref><ref name=Mindat>{{cite web | title=Aegirine | website=Mindat.org | url=https://www.mindat.org/min-31.html | access-date=9 August 2025}}</ref><ref name=Webmin>{{cite web | title=Aegirine Mineral Data | website=Mineralogy Database | url=https://webmineral.com/data/Aegirine.shtml | access-date=9 August 2025}}</ref><ref name=Hurlbut>Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''[https://archive.org/details/manualofmineralo00klei/page/n13/mode/2up Manual of Mineralogy]'', 20th ed., {{ISBN|0-471-80580-7}} (via Internet Archive</ref> }}

'''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.

==Etymology== The name ''aegirine'' is derived from Ægir, a Norse mythological figure (god of the sea), as the mineral was first described from Norway.<ref name=Handbook/><ref name=Mindat/>

A synonym for the mineral is ''acmite'' (from Greek ἀκμή "point, edge") in reference to the typical pointed crystals.<ref>{{Cite EB1911|wstitle=Acmite|volume=1|page=149|short=y}}</ref>

==Chemistry and description== [[File:Aegirine - Acmite in syenite Sodium iron silicate Magnet Cove Hot Springs County Arkansas 2000.jpg|thumb|left|Syenite with aegirine and acmite from Magnet Cove, Arkansas, US]] Aegirine is the sodium endmember of the aegirine–augite series.{{cn|date=August 2025}}

It has the chemical formula NaFeSi<sub>2</sub>O<sub>6</sub>, in which the iron is present as the ion Fe<sup>3+</sup>. 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.{{cn|date=August 2025}}

Aegirine occurs as dark green monoclinic prismatic crystals.<ref name=Mindat/> It has a glassy luster and perfect cleavage, "in two directions at near 90 degree angles".<ref name=galleries/> 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.<ref name=Mindat/><ref name=Webmin/>

Associated minerals include augite, nepheline, andradite, baryte, quartz, spessartine, riebeckite, biotite, sodalite, and albite.<ref name=galleries/>

==Occurrence== The acmite variety was first described in 1821, at Kongsberg, Norway,<ref>{{cite book| last = Dana | first = James Dwight | title = Manual of Mineralogy | year = 1855 | orig-year = 1837 | edition = 7th | publisher = Durrie & Peck | location = Philadelphia, PA}}</ref> and the aegirine variety in 1835 for an occurrence in Rundemyr, Øvre Eiker, Buskerud, Norway.<ref name=Mindat/>

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.<ref name=Handbook/>

Major localities include Mont Saint-Hilaire, Quebec, Canada; Kongsberg, Norway; Narsarssuk, Greenland; Kola Peninsula, Russia; Magnet Cove, Arkansas, US; Kenya; Scotland, and Nigeria.<ref name=galleries>{{cite web | title=AEGIRINE (Sodium Iron Silicate) | website=mineral.galleries.com | url=http://mineral.galleries.com/minerals/silicate/aegirine/aegirine.htm | archive-url=https://web.archive.org/web/20050507101037/http://mineral.galleries.com/minerals/silicate/aegirine/aegirine.htm | archive-date=7 May 2005 | url-status=dead | access-date=9 August 2025}}</ref>

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.<ref>{{cite journal | last1=Jago | first1=James B. | last2=Pharaoh | first2=Mark D. | title=Pre-Antarctic Mawson in South Australia and western New South Wales | journal=Transactions of the Royal Society of South Australia | publisher=Informa UK | volume=140 | issue=1 | date=2 January 2016 | issn=0372-1426 | doi=10.1080/03721426.2016.1149323 | pages=107–128| bibcode=2016TRSAu.140..107J | url=https://www.researchgate.net/publication/297672396}}</ref><ref>"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. </ref>

==Uses== Aegirine is sometimes used as a gemstone.<ref>{{cite book | last=Manutchehr-Danai | first=Mohsen | title=Dictionary of Gems and Gemology | publisher=Springer Science & Business Media | date=9 March 2013 | isbn=978-3-662-04288-5 | url=https://books.google.com/books?id=2UX1CAAAQBAJ | page=5}}</ref>

==See also== * List of minerals

==References== {{Reflist}}

==External links== * [https://web.archive.org/web/20050507101037/http://mineral.galleries.com/minerals/silicate/aegirine/aegirine.htm Mineral Galleries] {{commons}}

Category:Sodium minerals Category:Iron(III) minerals Category:Monoclinic minerals Category:Minerals in space group 15 Category:Gemstones Category:Minerals described in 1821 Category:Clinopyroxene subgroup