Pyrrhotite
Pyrrhotite (pyrrhos in Greek meaning "flame-coloured") is an iron sulfide mineral with the formula Fe(1-x)S (x = 0 to 0.125). It is a nonstoichiometric variant of FeS, the mineral known as troilite. Pyrrhotite is also called magnetic pyrite, because the color is similar to pyrite and it is weakly magnetic. The magnetism decreases as the iron content decreases, and troilite is non-magnetic. Pyrrhotite is generally tabular and brassy/bronze in color with a metallic luster. The mineral occurs with mafic igneous rocks like norites, and may form from pyrite during metamorphic processes. Pyrrhotite is associated and mined with other sulfide minerals like pentlandite, pyrite, chalcopyrite, and magnetite, and has been found globally.
| Pyrrhotite | |
|---|---|
Brassy, tabular crystals of pyrrhotite, with sphalerite and quartz, from Nikolaevskiy Mine, Primorskiy Kray, Russia. Specimen size: 5.3 × 4.1 × 3.8 cm | |
| General | |
| Category | Mineral |
| Formula (repeating unit) | Fe1−xS (x = 0 to 0.125) |
| IMA symbol | Pyh |
| Strunz classification | 2.CC.10 |
| Crystal system | Monoclinic, with hexagonal polytypes |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | A2/a |
| Unit cell | a = 11.88 Å, b = 6.87 Å, c = 22.79 Å; β = 90.47°; Z = 26 |
| Identification | |
| Color | Bronze, dark brown |
| Crystal habit | Tabular or prismatic in hexagonal prisms; massive to granular |
| Cleavage | Absent |
| Fracture | Uneven |
| Mohs scale hardness | 3.5 – 4.5 |
| Luster | Metallic |
| Streak | Dark grey – black |
| Specific gravity | 4.58 – 4.65, average = 4.61 |
| Refractive index | Opaque |
| Fusibility | 3 |
| Solubility | Soluble in hydrochloric acid |
| Other characteristics | Weakly magnetic, strongly magnetic on heating; non-luminescent, non-radioactive |
| References | |
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