sedimentary
Rounded dark river pebble
Likely fine-grained basalt or andesite; exact identification requires a fresh surface or tests
AI-generated identification · may be incorrectDark brown-gray, dull to slightly earthy luster, smooth water-worn surface, and no visible crystals or cleavage. Likely hardness about 5–6 Mohs and specific gravity roughly 2.7–3.0 if volcanic rock.
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Physical properties
Dark brown-gray, dull to slightly earthy luster, smooth water-worn surface, and no visible crystals or cleavage. Likely hardness about 5–6 Mohs and specific gravity roughly 2.7–3.0 if volcanic rock.
Formation & geological history
Probably an eroded and transported cobble shaped by stream or wave abrasion; its original volcanic age and formation setting cannot be determined from the image.
Uses & applications
Primarily a landscaping, craft, or collecting stone; if confirmed as basalt, crushed material is used for aggregate, road base, and concrete.
Geological facts
The rounded form reflects prolonged mechanical abrasion rather than crystal growth. Weathering can produce the brown coating while the interior remains gray-black.
Field identification & locations
Common in riverbeds, beaches, and glacial deposits. A streak test, magnetism check, specific-gravity measurement, and inspection of a broken or polished edge can distinguish basalt from other dark rocks.
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