igneous
Water-worn gray pebble, likely basalt
Possibly basalt, a fine-grained mafic volcanic rock
AI-generated identification · may be incorrectDark gray, dull to slightly silky surface, fine-grained and rounded by abrasion; basalt typically has Mohs hardness about 6 and consists mainly of plagioclase and pyroxene, often with olivine. The image alone cannot confirm its composition or crystal structure.
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Physical properties
Dark gray, dull to slightly silky surface, fine-grained and rounded by abrasion; basalt typically has Mohs hardness about 6 and consists mainly of plagioclase and pyroxene, often with olivine. The image alone cannot confirm its composition or crystal structure.
Formation & geological history
If basalt, it formed when lava cooled rapidly at or near Earth’s surface; the pebble’s smooth shape likely developed through river or beach transport. Its geological age cannot be determined from the photograph.
Uses & applications
Ordinary pebbles are mainly decorative or collectible; basalt is also used as crushed aggregate, paving stone, and construction material.
Geological facts
Basalt is the most common volcanic rock in Earth’s oceanic crust and forms extensive lava flows.
Field identification & locations
A compact, fine-grained texture and dark color support basalt, while its rounded edges indicate water wear; confirm in hand with a fresh surface or mineral testing. Basalt is widespread worldwide, especially in volcanic regions.
