metamorphic
Weathered iron-rich metamorphic rock (probable amphibolite or schist fragment)
Likely hornblende–plagioclase amphibolite with biotite/chlorite alteration; exact identification requires testing
AI-generated identification · may be incorrectDark brown-gray, fine- to medium-grained, dull to slightly silky luster, with weak foliation and rusty iron-oxide staining. Estimated hardness 5–6 Mohs; cleavage is not obvious and specific gravity is likely about 2.9–3.3.
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Physical properties
Dark brown-gray, fine- to medium-grained, dull to slightly silky luster, with weak foliation and rusty iron-oxide staining. Estimated hardness 5–6 Mohs; cleavage is not obvious and specific gravity is likely about 2.9–3.3.
Formation & geological history
Probably formed when basaltic or gabbroic rock was metamorphosed under moderate-to-high pressure and temperature, commonly during mountain building; its geological age cannot be determined from the photograph. Surface weathering produced the brown oxidation and rounded shape.
Uses & applications
Used locally as aggregate, riprap, or decorative stone; generally has little gemstone value unless unusually attractive or polished.
Geological facts
The specimen appears water-worn or strongly weathered, and the apparent banding may reflect metamorphic foliation rather than sedimentary layering.
Field identification & locations
Look for aligned dark amphibole or mica grains, a green-black interior on a fresh chip, and weak response to a steel scratch; it is not magnetic unless it contains appreciable magnetite. Common in metamorphic belts and stream gravels; a thin section or lab mineral analysis is needed for certainty.
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