Nichromite
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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]
| Nichromite | |
|---|---|
| |
| General | |
| Category | Spinel group |
| Formula | (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] |
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]