igneous
Weathered volcanic rock, likely andesite or basalt
Fine-grained volcanic silicate rock; composition cannot be confirmed visually
AI-generated identification · may be incorrectGray to brown, dull earthy luster, massive and fine-grained, with strongly weathered rough surfaces; likely Mohs hardness about 5–6 and specific gravity roughly 2.6–2.9. No clear crystals or cleavage are visible.
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Physical properties
Gray to brown, dull earthy luster, massive and fine-grained, with strongly weathered rough surfaces; likely Mohs hardness about 5–6 and specific gravity roughly 2.6–2.9. No clear crystals or cleavage are visible.
Formation & geological history
Formed when lava cooled at or near Earth’s surface, probably during a Cenozoic or older volcanic episode; the exact age and subtype require petrographic or chemical analysis. Surface texture reflects prolonged weathering and oxidation.
Uses & applications
Common volcanic rock is used as aggregate, riprap, road base, and occasionally building stone. This specimen has little jewelry value but may interest local collectors.
Geological facts
The apparent pale crust and cavities may represent alteration, vesicles, or weathering rather than a distinct mineral layer. A fresh broken surface would best reveal whether it is basalt, andesite, or another volcanic rock.
Field identification & locations
Look for a dense fine-grained interior, dark gray color, and absence of visible sand grains or layered bedding; a streak, acid, magnet, and thin-section test can help. Common in volcanic regions worldwide.
