metamorphic
Iron-oxide-stained sulfide-bearing rock, possibly pyrite-bearing schist
Likely quartz–mica schist or massive sulfide rock with pyrite (FeS₂) and limonite/goethite (FeO(OH)·nH₂O)
AI-generated identification · may be incorrectDark gray, fine- to medium-grained, irregularly foliated specimen with brassy-gold metallic patches and rusty yellow-brown weathering. Pyrite has Mohs hardness 6–6.5 and metallic luster; iron oxides are softer, earthy, and nonmetallic; exact identification requires a fresh surface and tests.
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Physical properties
Dark gray, fine- to medium-grained, irregularly foliated specimen with brassy-gold metallic patches and rusty yellow-brown weathering. Pyrite has Mohs hardness 6–6.5 and metallic luster; iron oxides are softer, earthy, and nonmetallic; exact identification requires a fresh surface and tests.
Formation & geological history
Probably formed when sulfide minerals crystallized in hydrothermal veins or metamorphosed volcanic/sedimentary material, then oxidized near the surface. The age cannot be determined from the photograph and depends on its locality.
Uses & applications
Pyrite-bearing rocks may be collected for mineral specimens and historically processed for sulfur or associated metals; iron-oxide-rich material has little construction value.
Geological facts
Brassy areas may be pyrite, chalcopyrite, or weathered sulfide rather than gold. A streak test, hardness test, magnet test, and ideally X-ray diffraction or chemical analysis are needed for confident identification.
Field identification & locations
Look for metallic cubic pyrite crystals, pale green-black streak for pyrite, or a greenish-black streak and softer surface for chalcopyrite; gold leaves a yellow streak and is malleable. Common settings include hydrothermal veins and metamorphic sulfide deposits.
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