igneous
Possible basalt or weathered mafic rock
Fine-grained mafic igneous rock, likely basalt; exact identification requires testing
AI-generated identification · may be incorrectDark brown-black, rounded and highly weathered, with dull to faintly submetallic luster and no obvious crystals. Likely hardness about 5–6 Mohs, dense, massive, and lacking visible cleavage; the shape appears naturally water-worn.
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Physical properties
Dark brown-black, rounded and highly weathered, with dull to faintly submetallic luster and no obvious crystals. Likely hardness about 5–6 Mohs, dense, massive, and lacking visible cleavage; the shape appears naturally water-worn.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly during volcanic activity from the Precambrian to the present. Brown coloration likely reflects oxidation and surface weathering.
Uses & applications
Used as aggregate, roadstone, riprap, and occasionally as a decorative stone; this small specimen has mainly educational or modest collecting value.
Geological facts
Its unusually smooth, lobed form is consistent with stream or beach abrasion, though it could also be a fragment of another dark volcanic rock such as andesite or basaltic scoria.
Field identification & locations
Look for a black-to-gray fine-grained interior, high density, and possible tiny feldspar crystals; a streak test, magnet response, and fresh-break inspection would help. Common worldwide in volcanic regions and gravel deposits.
