Cohenite

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Cohenite
General
Category Native element mineral, carbide
Formula
(repeating unit)
(Fe,Ni,Co)3C
Strunz classification 01.BA.05
Crystal symmetry Orthorhombic dipyramidal
H-M symbol: (2/m 2/m 2/m)
Space group: Pbnm
Unit cell a = 5.09 Å, b = 6.74 Å, c = 4.52 Å; Z=4
Identification
Color Tin-white; oxidizes to light bronze then golden yellow
Crystal habit Platy to needlelike crystals; also as rims on or in dendritic intergrowths with iron
Crystal system Orthorhombic
Cleavage Good on {100}, {010}, and {001}
Tenacity Brittle
Mohs scale hardness 5.5–6
Luster Metallic
Diaphaneity Opaque
Specific gravity 7.2 – 7.65
Other characteristics Strongly magnetic
References [1][2][3]

Cohenite is a naturally occurring iron carbide mineral with the chemical structure (Fe, Ni, Co)3C. This forms a hard, shiny, silver mineral which was named by E. Weinschenk in 1889 after the German mineralogist Emil Cohen, who first described and analysed material from the Magura meteorite found near Slanica, Žilina Region, Slovakia.[1] Cohenite is found in rod-like crystals in iron meteorites.[4]

On Earth cohenite is stable only in rocks which formed in a strongly reducing environment and contain native iron deposits. Such conditions existed in some places where molten magmas invaded coal deposits, e.g. on Disco Island in Greenland, or at the Bühl near Kassel in Germany.[3]

Associated minerals include native iron, schreibersite, troilite and wustite.[3]

Similar iron carbides occur also in technical iron alloys and are called cementite.

See also[edit]

References[edit]

  1. ^ a b Mindat.org Cohenite
  2. ^ Webmineral.com Cohenite
  3. ^ a b c Handbook of Mineralogy
  4. ^ Vagn F. Buchwald, Handbook of Iron Meteorites, University of California Press, 1975 ISBN 978-0520029347