Millerite
Millerite is a nickel sulfide mineral, NiS. It is brassy in colour and has an acicular habit, often forming radiating masses and furry aggregates. It can be distinguished from pentlandite by crystal habit, its duller colour, and general lack of association with pyrite or pyrrhotite.
| Millerite | |
|---|---|
| General | |
| Category | Sulfide mineral |
| Formula (repeating unit) | NiS |
| IMA symbol | Mlr |
| Strunz classification | 2.CC.20 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) (same H-M symbol) |
| Space group | R3m |
| Unit cell | a = 9.607 Å, c = 3.143 Å; Z = 9 |
| Identification | |
| Colour | Pale brass-yellow to bronze-yellow, tarnishes to iridescence |
| Crystal habit | Typically acicular (needle-like) often in radial sprays – also massive |
| Cleavage | Perfect on {1011} and {0112} – obscured by typical form |
| Fracture | Uneven |
| Tenacity | Brittle; capillary crystals elastic |
| Mohs scale hardness | 3–3.5 |
| Luster | Metallic |
| Streak | Greenish black |
| Diaphaneity | Opaque |
| Specific gravity | 5.3–5.5 |
| Other characteristics | brittle and becomes magnetic on heating |
| References | |
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