Nichromite

Nichromite
General
Category Spinel group
Formula
(repeating unit)		 (Ni,Co,Fe)(Cr,Fe,Al)2O4
Strunz classification 4.BB.05
Crystal system Isometric
Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space group Fd3m
Unit cell a = 8.32 Å; V = 573.86 Å3; Z = 8
Identification
Color Dark green, black
Crystal habit Granular, anhedral to subhedral
Fracture Conchoidal
Mohs scale hardness 6-​6 1⁄2
Luster Metallic
Streak Greyish green
Diaphaneity Opaque
Specific gravity 5.10
Optical properties Isotropic
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

  1. 1 2 3 Nichromite on Mindat.org
  2. 1 2 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. 1 2 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.
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