Nichromite: Properties and Occurrences

Nichromite (Ni, Co, Fe)(Cr, Fe, Al)2O4 is a black cubic metallic mineral and a member of the spinel group. It is an isometric-hexoctahedral black mineral containing aluminum, chromium, cobalt, iron, nickel, and oxygen. The spinel group minerals have been the focus of many studies, not only because of their economic interest but also due to the fact that they are very useful as petrogenetic indicators.

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.

General Information

  • Category: Spinel group
  • Formula: (repeating unit) (Ni,Co,Fe)(Cr,Fe,Al)2O4
  • Crystal system: Isometric
  • Crystal class: Hexoctahedral (m3m)
  • Color: Dark green, black.

Properties

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.

  • 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

Occurrences

Nichromite was originally reported from the Bon Accord nickel deposit in Barberton District, South Africa. Occurring naturally in a nickel deposit, nichromite is named for chromite with dominant nickel. It was originally reported from the Bon Accord nickel deposit in Barberton District, South Africa.

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