Cohenite

Iron carbide mineral
(repeating unit)(Fe,Ni,Co)3CIMA symbolCoh[1]Strunz classification1.BA.05Crystal systemOrthorhombicCrystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)Space groupPnmaUnit cella = 5.09 Å, b = 6.74 Å,
c = 4.52 Å; Z = 4IdentificationColorTin-white; oxidizes to light bronze then golden yellowCrystal habitPlaty to needlelike crystals; also as rims on or in dendritic intergrowths with ironCleavageGood on {100}, {010}, and {001}TenacityBrittleMohs scale hardness5.5–6LusterMetallicDiaphaneityOpaqueSpecific gravity7.2–7.65Other characteristicsStrongly magneticReferences[2][3][4][5]

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.[3] Cohenite is found in rod-like crystals in iron meteorites.[6]

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 Disko Island in Greenland, or at the Bühl near Kassel in Germany.[5]

Associated minerals include native iron, schreibersite, troilite and wustite.[5]

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

See also

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Mineralienatlas
  3. ^ a b Mindat.org Cohenite
  4. ^ Webmineral.com Cohenite
  5. ^ a b c Handbook of Mineralogy
  6. ^ Vagn F. Buchwald, Handbook of Iron Meteorites, University of California Press, 1975 ISBN 978-0520029347
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