igneous
Rounded dark pebble, likely basalt or greenstone
Probable basalt (fine-grained mafic volcanic rock); exact identification requires testing
AI-generated identification · may be incorrectDark gray-green to brown, dull to slightly earthy luster, fine-grained and massive, with no visible crystals or cleavage; typical hardness about 5–6 Mohs and specific gravity about 2.8–3.1.
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Physical properties
Dark gray-green to brown, dull to slightly earthy luster, fine-grained and massive, with no visible crystals or cleavage; typical hardness about 5–6 Mohs and specific gravity about 2.8–3.1.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly during Cenozoic to recent volcanic activity; the rounded shape indicates transport and abrasion by water or glacial action.
Uses & applications
Common basalt is used as crushed aggregate, road stone, riprap, and occasionally landscaping material; an isolated pebble generally has negligible commercial value.
Geological facts
The photograph shows a small, naturally rounded specimen, but lighting and resolution prevent confident separation of basalt from weathered greenstone, amphibolite, or another dark river rock.
Field identification & locations
Look for a dense, fine texture, dark color, lack of layering, and possible tiny feldspar crystals; a streak test, magnetism test, fresh break, and close examination are useful. Common worldwide, especially in volcanic and river environments.
