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Pyrite vs Chalcopyrite: Hardness, Colour and Tarnish

Pyrite and chalcopyrite are brassy, metallic sulfides that commonly occur together. Streak can overlap, so hardness is usually the fastest separator. Pyrite is hard enough to scratch glass and normally resists a steel nail; chalcopyrite is softer, scratches with steel, and often develops an iridescent tarnish. Try a steel nail on a clean surface. Chalcopyrite, Mohs 3.5–4, scratches readily; pyrite, Mohs 6–6.5, usually resists. Pyrite commonly forms sharp cubes or striated crystals, while chalcopyrite is often massive and more richly yellow or iridescent. Inspect several fresh surfaces because weathering can change both colour and tarnish. Try a steel nail on an inconspicuous point. An easy scratch strongly favours chalcopyrite. Use expendable glass only if needed. A genuine groove supports pyrite; wipe away loose powder before deciding. Confirm with crystal form and tarnish. Sharp cubes or striated faces favour pyrite; massive iridescent material favours chalcopyrite. Record whether both minerals occur together rather than forcing a single identification on a mixed sulfide sample. Do not grind, heat, or acid-test sulfide minerals. Minimize dust, wash hands, and follow site hygiene procedures. Neither mineral establishes copper or gold grade. Economic conclusions require representative sampling and laboratory analysis. A weathered surface can hide diagnostic colour and hardness; use a small existing fresh edge instead of breaking a valuable specimen.