Pyrite
The mineral pyrite (/ˈpaɪraɪt/ PY-ryte), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula FeS2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
| Pyrite | |
|---|---|
Intergrowth of lustrous, cubic crystals of pyrite, with some surfaces showing characteristic striations, from Huanzala mine, Ancash, Peru. Specimen size: 7.0 × 5.0 × 2.5 cm | |
| General | |
| Category | Sulfide mineral |
| Formula (repeating unit) | FeS2 |
| IMA symbol | Py |
| Strunz classification | 2.EB.05a |
| Dana classification | 2.12.1.1 |
| Crystal system | Cubic |
| Crystal class | Diploidal (m3) H-M symbol: (2/m 3) |
| Space group | Pa3 |
| Unit cell | a = 5.417 Å, Z = 4 |
| Identification | |
| Formula mass | 119.98 g/mol |
| Color | Pale brass-yellow reflective; tarnishes darker and iridescent |
| Crystal habit | Cubic, faces may be striated, but also frequently octahedral and pyritohedral. Often inter-grown, massive, radiated, granular, globular, and stalactitic. |
| Twinning | Penetration and contact twinning |
| Cleavage | Indistinct on {001}; partings on {011} and {111} |
| Fracture | Very uneven, sometimes conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 6–6.5 |
| Luster | Metallic, glistening |
| Streak | Greenish-black to brownish-black |
| Diaphaneity | Opaque |
| Specific gravity | 4.95–5.10 |
| Density | 4.8–5 g/cm3 |
| Fusibility | 2.5–3 to a magnetic globule |
| Solubility | Insoluble in water |
| Other characteristics | paramagnetic |
| References | |
Pyrite's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold. The color has also led to the nicknames brass, brazzle, and brazil, primarily used to refer to pyrite found in coal.
The name pyrite is derived from the Greek πυρίτης λίθος (pyritēs lithos), 'stone or mineral which strikes fire', in turn from πῦρ (pyr), 'fire'. In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel; Pliny the Elder described one of them as being brassy, almost certainly a reference to what is now called pyrite.
By Georgius Agricola's time, c. 1550, the term had become a generic term for all of the sulfide minerals.
Pyrite is usually found associated with other sulfides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds and as a replacement mineral in fossils, but has also been identified in the sclerites of scaly-foot gastropods. Despite being nicknamed "fool's gold", pyrite is sometimes found in association with small quantities of gold. A substantial proportion of the gold is "invisible gold" incorporated into the pyrite (see Carlin-type gold deposit). It has been suggested that the presence of both gold and arsenic is a case of coupled substitution but as of 1997 the chemical state of the gold remained controversial.