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Aegirine (also known as Acmite)

Discovered in 1835.   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

NaFe³⁺(Si₂O₆)

Sodium Iron Silicate

Molecular Weight:

231.00 gm

Composition:

Sodium

9.95 %

Na

13.42 %

Na₂O

Iron

24.18 %

Fe

34.56 %

Fe₂O₃

Silicon

24.32 %

Si

52.02 %

SiO₂

Oxygen

41.56 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/F.01-140

Nickel-Strunz 10th Ed. ID:

9.DA.25

9 : SILICATES (Germanates)
D : Inosilicates
A : Inosilicates with 2-periodic single chains, Si₂O₆; pyroxene family

Related to:

Pyroxene Group. Clinopyroxene Subgroup.

Members of Group:

Pyroxene Group: Canaanite, Clinopyroxene Subgroup, Orthopyroxene Subgroup

Members of Subgroup:

Clinopyroxene Subgroup: Aegirine, Augite, Clinoenstatite, Clinoferrosilite, Diopside, Essenite, Grossmanite, Hedenbergite, Jadeite, Jervisite, Johannsenite, Kanoite, Kosmochlor, Kushiroite, Namansilite, Natalyite, Petedunnite, Pigeonite, Spodumene

Varieties:

Urbanite, Vanadian Aegirine

Synonyms:

Acmite, Acnite, Aegerine, Aegerite, Aegirite, Aegyrina, Aegyrine, Aegyrite, Aemite, Agirine, Jadeite-Aegirine, Natronägirin, Soda-Aegirite

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Prismatic crystals, with blunt to steep terminations, to 35 cm, striated lengthwise, can be bent or twisted. In sprays of acicular crystals, fibrous, in radial concretions.

Twinning:

Simple and lamellar twinning common.

Physical Properties

Cleavage:

Distinct; Good on {110}, Parting on {100}

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

6.0

Density:

3.50 - 3.60 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Green, Dark Green, Greenish Black, Black, Reddish Brown

Transparency:

Translucent to Opaque

Luster:

Vitreous to Resinous

Refractive Index:

1.720 - 1.839  Biaxial ( - )

Birefringence:

0.037 - 0.061

Dispersion:

Moderate to Strong

Pleochroism:

X = emerald green, deep green; Y = grass-green, deep green, yellow; Z = brownish green, green, yellowish brown, yellow

Occurances

Geological Setting:

Common in alkalic igneous rocks, carbonatites, and pegmatites. From regionally metamorphosed schists, gneisses, and iron formations; in blueschist facies rocks, and from sodium metasomatism in granulites. An authigenic mineral in some shales and marls.

Common Associations:

Potassic Feldspar, Nepheline, Riebeckite, Arfvedsonite, Aenigmatite, Astrophyllite, Catapleiite, Eudialyte, Sérandite, Apophyllite

Common Impurities:

Al, Ti, V, Mn, Mg, Ca, K, Zr, Ce

Co-Type Localities:

• Rundemyr, Nedre Eiker, Buskerud, Norway
• Låven, Langesundsfjorden, Larvik, Vestfold, Norway

Year Discovered:

1835

View mineral photos:

Aegirine Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Aegirine, also known as Acmite, is a member of the Pyroxene Group of minerals that includes Aegirine, Diopside, Hedenbergite, Hypersthene, Jadeite, Petedunnite and Spodumene. Aegirine is a fairly common mineral, but rarely available as a gem. Not that gems would be that rare, just that they are not particularily attractive and would only be faceted for the sake of collecting. Gems are very dark green to greenish-black, almost opaque and usually very heavily included. 

Aegirine is named after Aegir, the Teutonic (Scandanavian) god of the sea. A synonym for the mineral is Acmite, from the Greek word akme for "point" in reference to the typical pointed crystals.

Current mineral sources are Mont Saint-Hilaire, Quebec, Canada; Mt. Malosa, Zomba District, Malawi; Kongsberg, Norway; Narsarssuk, Greenland; Kola Peninsula, Russia and Magnet Cove, Arkansas, USA.

Aegirine gems for sale:

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