igneous
Dark gray water-worn pebble
Likely basalt or another fine-grained mafic rock; exact identification is not possible from the image alone
AI-generated identification · may be incorrectDark gray-green, rounded, and apparently fine-grained with a dull to slightly smooth surface. If basalt, it is typically Mohs 5–6, made chiefly of plagioclase and pyroxene, and has no visible cleavage.
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Physical properties
Dark gray-green, rounded, and apparently fine-grained with a dull to slightly smooth surface. If basalt, it is typically Mohs 5–6, made chiefly of plagioclase and pyroxene, and has no visible cleavage.
Formation & geological history
A likely basalt pebble formed when mafic lava cooled, then became rounded by water or other abrasion. Its age and source cannot be determined from the photo.
Uses & applications
Small pebbles are mainly collected or used decoratively; basalt is also used as aggregate and paving stone.
Geological facts
Basalt is the most common volcanic rock in Earth’s crust and commonly forms oceanic crust and lava flows.
Field identification & locations
Its dark color, fine texture, and rounded shape fit a water-worn basalt pebble, but grain size and a fresh, unweathered surface would help confirm it. Basalt occurs worldwide, especially in volcanic regions and river or beach gravels.
