igneous
Rounded dark river pebble, likely basalt
Fine-grained basalt (probable; exact identification requires examination)
AI-generated identification · may be incorrectDark gray to black, smooth and rounded by abrasion, with a fine-grained, subtly speckled surface. Basalt is typically Mohs 6, with a mostly matte to faintly waxy luster and no visible cleavage; the pebble’s texture is consistent with a dense volcanic rock.
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Physical properties
Dark gray to black, smooth and rounded by abrasion, with a fine-grained, subtly speckled surface. Basalt is typically Mohs 6, with a mostly matte to faintly waxy luster and no visible cleavage; the pebble’s texture is consistent with a dense volcanic rock.
Formation & geological history
Likely formed when mafic lava cooled rapidly at or near Earth’s surface, then was rounded by transport in water. Basalt occurs from ancient to recent geological ages.
Uses & applications
Commonly used as aggregate, road stone, and construction material; attractive pebbles are also collected or used decoratively.
Geological facts
Basalt is one of Earth’s most abundant volcanic rocks and makes up much of the ocean floor.
Field identification & locations
A dark, fine-grained, dense pebble with no obvious layering or large crystals supports basalt identification; similar-looking dark rocks can be difficult to distinguish by sight alone. Basalt is widespread, especially in volcanic regions and river or beach gravels.
