Åkermanite

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Åkermanite
Åkermanite, Calcite, Hillebrandite, Tilleyite - Mineralogisches Museum Bonn1.jpg
Åkermanite (yellowish brown), calcite (blue), foshagite (hillebrandite variety, fibrous), tilleyite (creamy)
General
CategorySorosilicates
Formula
(repeating unit)
Ca2Mg(Si2O7)
Strunz classification9.BB.10
Dana classification55.4.1.1 (8 ed)
Crystal systemTetragonal
Crystal classScalenohedral (42m)
H-M symbol: (4 2m)
Space groupP421m
Unit cella = 7.8288(8)
c = 5.0052(2) [Å]; Z = 2
Identification
ColorColorless, yellowish gray, green, brown
CleavageDistinct on {001}, poor on {110}
FractureIrregular/ uneven, conchoidal
TenacityBrittle
Mohs scale hardness5 - 6
LusterVitreous, resinous
StreakWhite
DiaphaneityTransparent, translucent
Specific gravity2.944
Optical propertiesUniaxial (+)
Refractive indexnω = 1.632 nε = 1.640
Birefringenceδ = 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[edit]

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