Pyrite cluster (iron pyrite)

Brassy yellow metallic luster with abundant cubic and pyritohedral crystals, striated faces, and uneven massive matrix. Mohs hardness 6–6.5; specific gravity about 5.0; opaque, brittle, with poor/indistinct cleavage.

Forms when iron-bearing fluids or sediments react with sulfur, commonly in hydrothermal veins, sedimentary rocks, and metamorphic environments. Individual crystals may form over millions of years; the specimen likely comes from a mineralized vein or sedimentary deposit.

Collected as a display mineral and used historically as a sulfur source; limited modern industrial use in sulfuric-acid production and mineral processing. Fine crystal clusters have decorative and educational value.

Its metallic color and cubic crystals earned it the nickname “fool’s gold,” but pyrite is harder and more brittle than gold and commonly tarnishes to iron oxides.

Identify by cubic/pyritohedral, striated crystals, brass-yellow color, high density, and inability to scratch with a steel knife easily; a streak test gives a greenish-black to brownish-black streak. Common localities include Peru, Spain, Italy, China, Mexico, and the United States.