Indistinct cleavage; uneven to conchoidal fracture
Core Principles & Analysis
Named from the Greek pyrites lithos ('stone which strikes fire'), pyrite produces sparks when struck against flint or steel and was used for fire-making from the Middle Paleolithic through 16th-century wheellock firearms.
In its cubic Pa3̄ crystal structure (solved by W. L. Bragg in 1913), low-spin divalent Fe²⁺ ions coordinate covalently bonded persulfide disulfide pairs (S₂²⁻), forming striated cubes, octahedra, and 12-faced pyritohedra.
Nicknamed 'fool's gold' for its brassy luster, pyrite is distinguished from native gold by its brittle fracture, greenish-black streak, and Mohs hardness of 6–6.5, and its surface oxidation in coal and metal mines generates sulfuric acid mine drainage.