Pyrite in Shale
Pyrite (Iron Disulfide) · Mineral Specimen
Crystal System
Cubic (Isometric); habit often includes cubes, pyritohedrons, or as in this image, microcrystalline or massive coatings.
Mineral Group
Sulfides
Chemical Formula
FeS2
Formation Process
Commonly forms via hydrothermal replacement or precipitation in sedimentary environments under low-oxygen conditions (anoxic) where organic matter is present.
About This Crystal
This specimen shows a greyish sedimentary host rock (shale) with sparkling, brassy-yellow to silver-grey metallic coatings. The mineral appears as fine-grained druzy aggregates or thin films, exhibiting a strong metallic luster contrast against the dull, earthy matrix.
Physical Characteristics
Color: Brass-yellow or pale gold; Streak: Greenish-black to brownish-black; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 4.9–5.2; Luster: Metallic.
Optical Properties
Opaque; No refractive index (metallic); exhibit high reflectivity and a distinct yellow-white tint in reflected light microscopy.
Hardness & Durability
Origin Region
Globally distributed; notably extracted from Spain (Rio Tinto), Peru, and across sedimentary basins in North America and Europe.
Hardness & Durability
Mohs hardness: 6–6.5; brittle toughness; sensitive to moisture which can cause 'pyrite decay' (sulfuric acid formation).
Care & Maintenance
Keep in a dry, low-humidity environment to prevent oxidation. Clean with a dry brush; avoid water or ultrasonic cleaners which can exacerbate the breakdown of sulfur components.
Rarity & Value
Common; high-quality cubic specimens are valued by collectors, but massive or microcrystalline forms like this specimen have low commercial value.
Special Characteristics
Known as 'Fool's Gold' because of its metallic yellow color; occasionally displays 'pyrite rot' where it decomposes into sulfate minerals in humid air.
Lore & History
Historically used by ancient Romans as a source of sparks to start fires. In metaphysical traditions, it is believed to represent abundance, protection, and the promotion of willpower and focus.