Pyrite with Iron Oxides (Fool's Gold in Matrix)

Physical Properties

Hardness: 6-6.5 on Mohs scale; Color: Brassy yellow with reddish-brown oxidation; Luster: Metallic; Crystal Structure: Isometric/Cubic (often appearing granular in matrix); Cleavage: Indistinct; Specific Gravity: 4.9-5.2.

Formation & Geological History

Formed in hydrothermal veins, sedimentary rocks, or through contact metamorphism. It is common in various geological environments from the Precambrian to Cenozoic eras.

Uses & Applications

Historical source of sulfur and sulfuric acid. Today, it is primarily a collector's specimen and used in jewelry (as 'marcasite' when faceted), though it is also an minor ore of iron.

Geological Facts

Famous for being mistaken for gold during the Gold Rush. It is one of the most common sulfide minerals and can contain trace amounts of actual gold and arsenic.

Field Identification & Locations

Identify in the field by its brassy color, greenish-black streak (on a porcelain plate), and relative hardness (gold can be scratched by a knife, pyrite cannot). Commonly found worldwide in mining districts.

Identified on: 4/13/2026

Mode: Standard