Pyrite (Fool's Gold)
Pyrite · Mineral Specimen / Industrial Mineral
Crystal System
Cubic (Isometric); habit is commonly cubic, pyritohedral (twelve pentagonal faces), or octahedral. This specimen shows a massive/druzy aggregate of small crystals.
Mineral Group
Sulfides
Chemical Formula
FeS2
Formation Process
Hydrothermal, Magmatic, and Sedimentary. It often forms through chemical precipitation in oxygen-poor environments or hydrothermal fluid deposition.
About This Crystal
A brassy, pale yellow metallic mineral with a bright luster. This specimen is an aggregate of many small, interlocking cubic crystals manifesting a sparkling, druzy surface. It is opaque with a vitreous to metallic sheen.
Physical Characteristics
Color: Brass-yellow; Streak: Greenish-black to brownish-black; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 4.8–5.0; Magnetism: Weakly magnetic after heating; Fluorescence: Usually none.
Optical Properties
Opaque (no refractive index in the standard sense); metallic luster; non-pleochroic; no significant dispersion or light phenomena.
Hardness & Durability
Origin Region
Notable sources include Navajún, Spain (perfect cubes), Peru (large clusters), Italy, and the USA. Forms in hydrothermal veins and sedimentary rocks.
Hardness & Durability
Mohs Hardness: 6–6.5. It is relatively brittle and can strike sparks against steel. High durability compared to gold but sensitive to oxidation and moisture.
Care & Maintenance
Keep dry; moisture and humidity can lead to 'pyrite disease' (oxidation into sulfuric acid and iron sulfates). Clean with a soft brush; avoid water and chemicals. Store in a low-humidity environment.
Rarity & Value
Common and abundant worldwide. Value is generally low for massive specimens, though well-crystallized aesthetic pieces (like Spanish cubes) command higher prices. Usually untreated.
Special Characteristics
Known for generating sparks when struck against metal (pyrotechnic properties). Can exhibit 'striations' (parallel lines) on the crystal faces.
Lore & History
Historically used by Native Americans for mirrors and as a spark-starter. In lore, it is used as a stone of protection, willpower, and prosperity (often called a 'money stone').