Pyrite in Matrix (Fool's Gold)
Pyrite (Iron Disulfide) · Mineral Specimen / Industrial Mineral
Crystal System
Cubic (Isometric); typically forms as cubes, pyritohedrons, or octahedrons. In this specimen, it appears as massive to granular aggregates and small disseminated crystals within a matrix.
Mineral Group
Sulfides
Chemical Formula
FeS2 (Iron Disulfide), sometimes with trace amounts of Co, Ni, Sb, and Au
Formation Process
Primarily Hydrothermal (precipitating from hot, mineral-rich fluids in veins) or Sedimentary (formed by the action of bacteria in anaerobic conditions). It can also form through contact metamorphism.
About This Crystal
The specimen shows brassy, metallic yellow pyrite grains embedded in a dark, weathered grey-brown rock matrix. The pyrite displays a metallic luster with some visible cubic or granular habit. The matrix is opaque and appears somewhat earthy or microcrystalline with rust-colored oxidation (limonite/goethite) on the surface.
Physical Characteristics
Color: Brass-yellow (mineral), grey to brown (matrix); Streak: Greenish-black to brownish-black; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 4.9–5.2; Tenacity: Brittle; Fluorescence: None.
Optical Properties
Luster: Metallic; Diaphaneity: Opaque; Refractive Index: N/A (Opaque); Birefringence: None (Isotropic); Pleochroism: None.
Hardness & Durability
Origin Region
Global distribution; notable sources include Spain (Rio Tinto), Peru (Huaron), Italy (Elba), and the USA (Colorado). Commonly found in sedimentary rocks, hydrothermal veins, and metamorphic rocks.
Hardness & Durability
Mohs Hardness: 6–6.5 (for the pyrite grains). It is relatively hard for a sulfide but brittle, meaning it can shatter under impact. Not recommended for high-wear jewelry because it can oxidize (tarnish or rust) when exposed to moisture.
Care & Maintenance
Keep dry; sensitive to high humidity and water which can cause 'pyrite disease' (oxidation into sulfuric acid and iron sulfates). Clean only with a dry soft brush or cloth. Store in a low-humidity environment away from delicate minerals.
Rarity & Value
Common; Value is generally low for massive/granular specimens. Rarity and price increase significantly for perfect, large cubic crystals or those with unique habits. It is frequently sold as an affordable decorative mineral.
Special Characteristics
Possesses semi-conductor properties; shows sparks when struck against steel (giving it its name from the Greek 'pyr' for fire). Sometimes contains microscopic inclusions of gold (Auriferous Pyrite).
Lore & History
Historically used by ancient civilizations for fire-starting and by Native Americans as polished mirrors. Known as 'Fool\'s Gold' because its metallic luster often deceived prospectors. Traditionally associated with the Solar Plexus chakra, believed to represent wealth, protection, and logical thinking.