igneous
Polished black pebble, likely basalt
Basalt (fine-grained mafic volcanic rock; visual identification is uncertain)
AI-generated identification · may be incorrectDark gray to black, rounded and polished, with a smooth, locally reflective surface. Basalt is typically fine-grained and composed mainly of plagioclase and pyroxene, sometimes with olivine; hardness is roughly 6 on the Mohs scale and specific gravity about 2.8–3.0.
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Physical properties
Dark gray to black, rounded and polished, with a smooth, locally reflective surface. Basalt is typically fine-grained and composed mainly of plagioclase and pyroxene, sometimes with olivine; hardness is roughly 6 on the Mohs scale and specific gravity about 2.8–3.0.
Formation & geological history
Basalt forms when mafic lava cools at or near Earth’s surface; its age depends on source. The pebble’s rounded shape likely results from prolonged transport and abrasion in water.
Uses & applications
Polished basalt pebbles are used in decorative landscaping, crafts, and collections; basalt is also widely used as aggregate and paving stone.
Geological facts
Basalt is Earth’s most abundant volcanic rock and forms much of the ocean floor.
Field identification & locations
A dense, dark, fine-grained appearance supports basalt identification, but the photo alone cannot rule out another dark stone. Common as stream, beach, and volcanic-field pebbles worldwide.
