igneous
Rounded dark river pebble, likely basalt
Basalt (fine-grained mafic volcanic rock; commonly plagioclase, pyroxene, and olivine)
AI-generated identification · may be incorrectDark gray to brown, weathered, dull to faintly granular luster; typically massive with no visible crystals or cleavage. Hardness about 5–6 Mohs; specific gravity approximately 2.8–3.0.
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Physical properties
Dark gray to brown, weathered, dull to faintly granular luster; typically massive with no visible crystals or cleavage. Hardness about 5–6 Mohs; specific gravity approximately 2.8–3.0.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. This specimen is water-rounded and may be geologically young or reworked from older volcanic rock.
Uses & applications
Used as crushed aggregate, road stone, railway ballast, riprap, and dimension stone; attractive polished pieces are used decoratively. Common specimens generally have little commercial or collector value.
Geological facts
The rounded shape indicates prolonged abrasion in a stream, beach, or glacial environment. Weathering can produce brown or rusty surface patches from iron-bearing minerals.
Field identification & locations
Look for dark color, substantial density, fine texture, and lack of layering; a streak, magnet test, and fresh broken surface can help distinguish it from andesite or slag. Common worldwide, especially near volcanic and formerly volcanic regions.
