Oldhamite
Oldhamite is a calcium magnesium sulfide mineral with the chemical formula (Ca,Mg)S. Ferrous iron may also be present in the mineral resulting in the chemical formula (Ca,Mg,Fe)S. It is a pale to dark brown accessory mineral in meteorites. It crystallizes in the cubic crystal system, but typically occurs as anhedral grains between other minerals.
| Oldhamite | |
|---|---|
Oldhamite (field of view: 1.5 cm) | |
| General | |
| Category | Sulfide mineral |
| Formula (repeating unit) | (Ca,Mg)S |
| IMA symbol | Old |
| Strunz classification | 2.CD.10 |
| Crystal system | Cubic |
| Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m) |
| Space group | Fm3m |
| Unit cell | a = 5.69 Å; Z = 4 |
| Identification | |
| Color | Pale chestnut-brown |
| Crystal habit | Crystal nodules, anhedral grains |
| Cleavage | Good on {001} |
| Mohs scale hardness | 4 |
| Luster | Sub-metallic |
| Diaphaneity | Transparent |
| Specific gravity | 2.58 |
| Optical properties | Isotropic |
| Refractive index | n = 2.137 |
| Fusibility | 2450 °C |
| Alters to | Tarnishes on exposure to moist air |
| References | |
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