igneous
Rounded dark river pebble
Likely basalt or a basaltic volcanic rock; exact identification requires a fresh surface and tests
AI-generated identification · may be incorrectFine-grained, dark gray-brown, dull to weakly earthy luster, rounded by water abrasion; likely hardness about 5–6 Mohs, with no visible cleavage and very low porosity. Mineral composition probably plagioclase, pyroxene, and minor iron-titanium oxides.
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Physical properties
Fine-grained, dark gray-brown, dull to weakly earthy luster, rounded by water abrasion; likely hardness about 5–6 Mohs, with no visible cleavage and very low porosity. Mineral composition probably plagioclase, pyroxene, and minor iron-titanium oxides.
Formation & geological history
Likely formed when basaltic lava cooled rapidly at or near Earth’s surface, then weathered and became stream-rounded; commonly Cenozoic to recent, though older basalt is also widespread.
Uses & applications
Primarily a natural decorative or teaching specimen; basalt is widely used as crushed aggregate, paving stone, riprap, and occasionally building stone.
Geological facts
Basalt is the most abundant volcanic rock in Earth’s oceanic crust and commonly forms columnar joints and extensive lava flows.
Field identification & locations
Look for a uniformly fine texture, dark color, high density, and possible tiny pale plagioclase crystals; a streak, magnet test, density test, or fresh break would help distinguish it from andesite, slag, or dark sedimentary rock. Common along rivers and beaches near volcanic terrains.
