igneous
Rounded river pebble, likely basalt or dark volcanic rock
Fine-grained mafic igneous rock; possibly basalt (identification uncertain from photograph)
AI-generated identification · may be incorrectDark gray-brown, dull to weakly earthy luster, smooth water-worn surface, and no visible crystals or cleavage. Likely Mohs hardness about 5–6 and specific gravity roughly 2.8–3.1.
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Physical properties
Dark gray-brown, dull to weakly earthy luster, smooth water-worn surface, and no visible crystals or cleavage. Likely Mohs hardness about 5–6 and specific gravity roughly 2.8–3.1.
Formation & geological history
Probably formed when mafic lava cooled rapidly, producing microscopic plagioclase and pyroxene, then became rounded by stream or beach abrasion. Its geological age cannot be determined visually and may range from recent to ancient.
Uses & applications
Suitable mainly as a decorative pebble, landscaping stone, or educational specimen; ordinary pieces have negligible jewelry or industrial value.
Geological facts
The rounded shape indicates transport by flowing water, waves, or glacial action rather than its original volcanic form. A streak test, magnet test, and fresh-edge examination could help distinguish basalt from other dark rocks.
Field identification & locations
Common in volcanic and glacial regions worldwide, including Hawaii, Iceland, the Pacific Northwest, and many river gravels. Look for a fine texture, substantial weight, dark color, and occasional tiny pale feldspar crystals; exact identification requires testing.
