Pyrrhotite
Pyrrhotite is a fairly common mineral but rarely faceted as a gem. The chemical formula of Pyrrhotite is Fe7S8 and its molecular weight is 85.12 gm. It is opaque and has a bronzey to brassy color. Pyrrhotite is weakly magnetic. Pyrrhotite has a specific gravity of 4.58 – 4.65 (g/cm3) and the refractive index of none because it is Opaque. It is the next most common magnetic mineral to Magnetite. Massive Pyrrhotite is common and magnetism is sometimes the only way to distinguish it from other brassy colored sulfides such as Chalcopyrite, Marcasite, Pentlandite or Pyrite. Although massive material occurs at many localities worldwide, good crystals are rare.
| Category: | Mineral |
| Chemical Formula: | Fe7S8 |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals typically tabular or platy, to 40 cm; steep pyramidal faces or short pyramidal; as rosettes showing nearly parallel aggregation; commonly massive, granular. |
| Twinning: | On [1012] |
| Cleavage: | None observed; distinct Parting on [0001] |
| Fracture: | Uneven to Sub-Conchoidal |
| Tenacity: | Brittle |
| Hardness (Mohs): | 3.5 – 4.5 |
| Hardness (Vickers): | VHN = 373-409 (100g load) |
| Density: | 4.58 – 4.65 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioacitve |
| Other: | Magnetic; varying in intensity inversely with iron content. |
| Color: | Bronze Brown, Bronze Red, or dark Brown; tarnishes quickly, rarely to iridescence |
| Transparency: | Opaque |
| Luster: | Metallic |
| Refractive Index: | n/a (Opaque) |
| Birefringence: | n/a (Opaque) |
| Dispersion: | n/a (Opaque) |
| Pleochroism: | Weak |
| Anisotropism: | Strong |
