Pyrite
Pyrite · Mineral Specimen / Semi-Precious Gemstone
Crystal System
Cubic (Isometric); common habits include cubic, pyritohedral, and octahedral. This specimen is polished as a cabochon.
Mineral Group
Sulfides
Chemical Formula
FeS2 (Iron Disulfide)
Formation Process
Forms in igneous, metamorphic, and sedimentary environments, frequently through hydrothermal precipitation or biogenic reduction of sulfates in anaerobic sedimentary conditions.
About This Crystal
This specimen is a polished, oval-shaped cabochon displaying a brassy, metallic luster. It features a pale brass-yellow body color with darker, vein-like inclusions or host rock matrix (likely shale or limestone) appearing as matte black patches. The surface is highly reflective with a smooth, vitreous to metallic finish.
Physical Characteristics
Color: Pale brass-yellow. Streak: Greenish-black to brownish-black. Cleavage: Indistinct on {001}. Fracture: Conchoidal to uneven. Specific Gravity: 4.8–5.1. Fluorescence: None. It is a brittle mineral with a metallic luster.
Optical Properties
Opaque (not transparent). Isotropic. Luster: Metallic. Refractive Index: High (not measurable by traditional gemstone refractometers as it is opaque). No pleochroism.
Hardness & Durability
Origin Region
Prominent sources include Spain (Navajún), Peru (Huanzala), Italy, USA, and Russia. Found in a variety of geological settings from hydrothermal veins to sedimentary rocks.
Hardness & Durability
Mohs Hardness: 6–6.5. It is relatively hard but brittle and prone to fracturing if dropped. It is much harder than gold (which it often resembles).
Care & Maintenance
Keep dry; pyrite can oxidize (forming sulfuric acid and iron oxides) when exposed to high humidity (pyrite disease). Clean with a soft, dry cloth. Avoid ultrasonic cleaners and acidic chemicals.
Rarity & Value
Common. Value is generally low for massive/bulk material, though high-quality crystals with sharp terminations or unique inclusions are valued by collectors. Often used in 'marcasite' jewelry.
Special Characteristics
Notable for its metallic luster and 'Fool's gold' appearance. It is paramagnetic and can produce sparks when struck against steel (pyrophoric properties).
Lore & History
Historically used by the Greeks and Romans for fire-starting. In folklore, it is associated with abundance, wealth, and protection. It was famously mistaken for gold by early explorers of the Americas.