metamorphic
Weathered sulfide-bearing metamorphic rock (probable pyrite schist)
Quartz–mica schist with iron sulfides, chiefly pyrite (FeS₂), possibly chalcopyrite (CuFeS₂)
AI-generated identification · may be incorrectDark gray, irregular and weakly foliated, with metallic yellow brassy patches and dull brown weathering. Likely hardness 6–6.5 for pyrite, Mohs 3.5–4 for chalcopyrite; metallic luster, opaque, dense, and lacking obvious cleavage in the sulfides.
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Physical properties
Dark gray, irregular and weakly foliated, with metallic yellow brassy patches and dull brown weathering. Likely hardness 6–6.5 for pyrite, Mohs 3.5–4 for chalcopyrite; metallic luster, opaque, dense, and lacking obvious cleavage in the sulfides.
Formation & geological history
Likely formed when sedimentary material was regionally metamorphosed and sulfide minerals crystallized from hydrothermal fluids; the specimen’s exact geological age cannot be determined from the photograph.
Uses & applications
Primarily a collector specimen; pyrite and chalcopyrite are important sources of sulfur and copper, while the host rock has little commercial value. Avoid prolonged moisture because sulfides can oxidize and produce acidic stains.
Geological facts
The brassy mineral may be pyrite (“fool’s gold”) or chalcopyrite, which is softer and often develops blue-green iridescent tarnish. A definitive identification requires hardness, streak, density, and ideally chemical or X-ray testing.
Field identification & locations
Common in metamorphic and hydrothermal ore districts worldwide, including the Appalachians, western North America, Spain, Peru, and Australia. A steel scratch test and streak on unglazed porcelain can help distinguish sulfides, but testing may damage the specimen.
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