mineral
Iron-rich sulfide ore, likely pyrite-bearing gossan
Pyrite (FeS₂), possibly mixed with iron oxides/hydroxides and other sulfides
AI-generated identification · may be incorrectDark brown-black, metallic to earthy luster with brassy yellow patches and iridescent tarnish; likely Mohs hardness 6–6.5 for pyrite, generally lacking obvious cleavage. The porous, weathered surface suggests oxidation and variable specific gravity, commonly around 4.5–5 for pyrite-rich material.
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Physical properties
Dark brown-black, metallic to earthy luster with brassy yellow patches and iridescent tarnish; likely Mohs hardness 6–6.5 for pyrite, generally lacking obvious cleavage. The porous, weathered surface suggests oxidation and variable specific gravity, commonly around 4.5–5 for pyrite-rich material.
Formation & geological history
Likely formed in hydrothermal veins or sulfide-rich sedimentary ore, then exposed to weathering that oxidized the outer surface into a gossan. The exact age and locality cannot be determined from the photograph.
Uses & applications
Primarily a collector specimen and potential ore indicator; pyrite is used industrially as a sulfur source and historically for sulfuric-acid production, but this weathered piece has little commercial value.
Geological facts
Iridescent purple, blue, and gold tarnish can develop on sulfide minerals through surface oxidation. Yellow metallic areas may be pyrite, while the dark matrix could include iron oxides, marcasite, chalcopyrite, or other sulfides.
Field identification & locations
Look for dense weight, metallic reflections, brassy cubic or granular crystals, and a dark streak; pyrite leaves a greenish-black to brown-black streak, unlike gold’s yellow streak. Avoid grinding or acid testing without protection because sulfide dust and oxidation products can be hazardous.
