Åkermanite

Åkermanite

Åkermanite (yellowish brown), calcite (blue), foshagite (hillebrandite variety, fibrous), tilleyite (creamy)
General
Category Sorosilicates
Formula
(repeating unit)		 Ca2Mg(Si2O7)
Strunz classification 9.BB.10
Dana classification 55.4.1.1 (8 ed)
Crystal system Tetragonal
Crystal class Scalenohedral (42m)
H-M symbol: (4 2m)
Space group P421m
Unit cell a = 7.8288(8)
c = 5.0052(2) [Å]; Z = 2
Identification
Color Colorless, yellowish gray, green, brown
Cleavage Distinct on {001}, poor on {110}
Fracture Irregular/ uneven, conchoidal
Tenacity Brittle
Mohs scale hardness 5 - 6
Luster Vitreous, resinous
Streak White
Diaphaneity Transparent, translucent
Specific gravity 2.944
Optical properties Uniaxial (+)
Refractive index nω = 1.632 nε = 1.640
Birefringence δ = 0.008
References [1][2]

Åkermanite (Ca2Mg[Si2O7]) is a melilite mineral of the sorosilicate group, containing calcium, magnesium, silicon, and oxygen. It is a product of contact metamorphism of siliceous limestones and dolostones, and rocks of sanidinite facies. Sanidinite facies represent the highest conditions of temperature of contact metamorphism and are characterized by the absence of hydrous minerals. It has a density of 2.944 g/cm3.[3][2] Åkermanite ranks a 5 or 6 on the Mohs scale of mineral hardness, and can be found gray, green, brown, or colorless. It has a white streak and a vitreous or resinous luster. It has a tetragonal crystal system and a good, or distinct, cleavage. It is the end member in a solid solution series beginning with gehlenite (Ca2Al[AlSiO2]).[1]

The mineral is named for Anders Richard Åkerman (1837–1922), a Swedish metallurgist. It has been found at Monte Somma and Vesuvius, and Monte Cavalluccio near Rome. It was "grandfathered" in as a species of mineral because it was described prior to 1959, before the founding of the International Mineralogical Association.[2]

References

  1. 1 2 "Åkermanite: Åkermanite mineral information and data.". mindat.org. Retrieved October 30, 2007.
  2. 1 2 3 "Akermanite Mineral Data". webmineral.com. Retrieved October 30, 2007.
  3. ↑ "Contact Metamorphism". tulane.edu. Retrieved October 30, 2007.
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