igneous
Likely weathered basalt with iron-oxide alteration
Basalt (fine-grained mafic volcanic rock), chiefly plagioclase and pyroxene with altered iron-bearing minerals
AI-generated identification · may be incorrectDark gray-black, fine-grained, massive, and weakly to moderately lustrous from weathering; brown-red surfaces indicate iron oxides. Typical hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.8–3.1.
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Physical properties
Dark gray-black, fine-grained, massive, and weakly to moderately lustrous from weathering; brown-red surfaces indicate iron oxides. Typical hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.8–3.1.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic provinces and ancient flood-basalt terrains. The reddish-brown rind and surface sheen likely developed through oxidation and weathering; exact age cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, roadstone, railway ballast, riprap, and occasionally dimension stone. This specimen has modest collector value unless it proves to be an unusual ore or impact-related rock.
Geological facts
The curved pale lines may be veins or cooling/weathering fractures, while the metallic-looking flecks are probably reflected light from altered mafic minerals rather than native metal.
Field identification & locations
Test with a steel knife: basalt is generally scratched weakly or not at all; it usually does not fizz with dilute acid and commonly leaves a gray streak. Basalt is plausible around 9.5°N, 44.1°E, where volcanic and mafic rocks occur regionally, but the image alone cannot distinguish it from dark metamorphic rock.
