Mineral Types - Aegerine

Name

First described as acmit by P. H. Ström (1821) from Rundemyr, Øvre Eiker, Buskerud, Norwayfor a mineral earlier mentioned shortly by Strøm (1784, as "crystalliseret hornsteen eller brun kantet og riflet Schoel i quarz" (crystallized hornstone or brownish angular and grooved schorl in quartz)). Ström (1821) recognized it as a new mineral and suggested the name wernerin, after the german geologist, Abraham Gottlob Werner. But Berzelius (1821), who analyzed the mineral, named it achmit after the greek αχμη, spear point, due to the habit of the crystals. < br /> Later, in 1834, the priest and mineralogist Hans Morten Thrane Esmark found a new mineral on Låven, Langesundsfjorden, Norway which was described and given the name aegirine, after Ægir (Aegir), the sea god in Norse mythology because the type location was along the sea shore (Berzelius 1835). Acmite and aegirine were first believed to be two separate species, one belonging to the amphiboles (acmite) and the other to the pyroxenes (aegirine). This was the case until 1871 when G. Tschermak put forward evidence that acmite and aegirine both belonged to the pyroxenes and are the same mineral. Acmite has been considered as a variety of aegirine (historically acmite had priority, so it should have been the other way around).

Physical Properties

Lustre: Vitreous
Transparency: Transparent, Opaque
Colour: Dark green to greenish black, reddish brown, black
Streak: Pale yellowish grey
Hardness: 6 on Mohs scale 
Tenacity: Brittle
Cleavage: Distinct/Good Good on {110}
Parting: on {100}
Fracture: Irregular/Uneven
Density: 3.5 - 3.6 g/cm3 (Measured) 3.576 g/cm3 (Calculated)

Chemical Properties

Formula: NaFe3+Si2O6
Elements listed: Fe, Na, O, Si
Common Impurities: Al,Ti,V,Mn,Mg,Ca,K,Zr,Ce

Crystallography

Crystal System: Monoclinic
Class (H–M): 2/m - Prismatic
Space Group: B2/b
Morohology: Prismatic crystals, showing 110, 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 on {100}

Synonyms

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

Varieties

Fedorovite, Titanian Aegirine, and Vanadian Aegirine