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Nichromite

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Nichromite
General
CategorySpinel group
Formula
(repeating unit)
(Ni,Co,Fe)(Cr,Fe,Al)2O4
Strunz classification4.BB.05
Crystal systemIsometric
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupFd3m
Unit cella = 8.32 Å; V = 573.86 Å3; Z = 8
Identification
ColorDark green, black
Crystal habitGranular, anhedral to subhedral
FractureConchoidal
Mohs scale hardness6-6+12
LusterMetallic
StreakGreyish green
DiaphaneityOpaque
Specific gravity5.10
Optical propertiesIsotropic
References[1][2][3][4]

Nichromite (Ni,Co,Fe)(Cr,Fe,Al)2O4[1] is a black cubic metallic mineral and member of the spinel group.[5] Nichromite was originally reported from the Bon Accord nickel deposit in Barberton District, South Africa.[1] Occurring naturally in a nickel deposit, nichromite is named for chromite with dominant nickel.[2]

The atomic arrangement of the spinel group is a commonly studied structure and characteristically has four closely packed oxygen atoms. The nickel atoms are organized corresponding to a "normal" spinel arrangement.[6]

The mineral has only been found in the Bon Accord Nickel Deposit in South Africa where it is formed by replacing chromite and rimmed by trevorite.[4]

References

[edit]
  1. ^ a b c Nichromite on Mindat.org
  2. ^ a b Nichromite on Webmineral
  3. ^ Sawaokaa,A.,Saitoa,S.,Inoueb,K. and Asadab,T. (1971)Effect of high pressure on the lattice constants of chromites having the spinel structure. Materials Research Bulletin, 6, 97-101.
  4. ^ a b Cabri, L. J., Chao G.Y., Pabst, Adolf, Fleischer, Michael. (1980) New Mineral Names. American Mineralogist, 65, 811.
  5. ^ Glossary of Geology
  6. ^ Wyckoff, R.W.G. (1965) Crystal Structures (Second Edition). 75-86 p. University of Arizona, Tucson, Arizona.