igneous
Vesicular basalt (likely weathered scoria)
Basaltic volcanic rock; chiefly plagioclase, clinopyroxene, and olivine with vesicles
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to slightly earthy luster, with abundant rounded gas cavities and irregular fracture. Typical hardness is about 5–6 Mohs; no obvious cleavage; specific gravity commonly 2.6–2.9, reduced by vesicles.
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Physical properties
Dark gray-brown, fine-grained, dull to slightly earthy luster, with abundant rounded gas cavities and irregular fracture. Typical hardness is about 5–6 Mohs; no obvious cleavage; specific gravity commonly 2.6–2.9, reduced by vesicles.
Formation & geological history
Formed when basaltic lava erupted and cooled rapidly, trapping gas bubbles; weathering produced the brown surface. Basaltic volcanism is geologically widespread, though this small specimen’s exact age cannot be determined visually.
Uses & applications
Used as aggregate, riprap, landscaping stone, and occasionally abrasive material; attractive scoria is collected, but this piece has little gem or commercial value.
Geological facts
The holes are vesicles, not fossil cavities. Very porous specimens may be called scoria; denser, finer-grained material is vesicular basalt.
Field identification & locations
Consistent with volcanic rock, but the image does not show diagnostic crystals. Near 46.7°N, 92.0°W, glacially transported basalt and basaltic cobbles are plausible, although local bedrock is varied; test for a dark streak, relatively high density, and lack of fizz in dilute acid.
