igneous
Rounded gray pebble, likely basalt or fine-grained igneous rock
Probably basalt (plagioclase feldspar + pyroxene ± olivine)
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to slightly silky surface; estimated Mohs hardness 5–6, massive texture, no visible cleavage, and moderate-to-high density. Its smooth shape indicates natural water abrasion or tumbling.
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Physical properties
Dark gray-green, fine-grained, dull to slightly silky surface; estimated Mohs hardness 5–6, massive texture, no visible cleavage, and moderate-to-high density. Its smooth shape indicates natural water abrasion or tumbling.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust; individual formation ages vary widely from recent to billions of years. The pebble was likely transported and rounded by a stream, beach, or glacial process.
Uses & applications
Common basalt is used for aggregate, road stone, riprap, and occasionally decorative landscaping; this small pebble has little commercial or jewelry value.
Geological facts
The specimen’s exact identity cannot be confirmed from a photograph alone; similar rounded stones may be andesite, diabase, or gray metamorphic rock.
Field identification & locations
Look for a uniformly fine texture, dark color, lack of layering, and possible tiny pale feldspar grains; a streak, density, magnetism, and fresh broken surface would help distinguish it. Basalt is widespread worldwide, especially near volcanic regions and oceanic islands.
