igneous
Water-worn black pebble, likely basalt
Basalt (fine-grained mafic volcanic rock; identification from the image is provisional)
AI-generated identification · may be incorrectDark gray to black, smooth and rounded with a subdued glossy surface; basalt is typically composed of plagioclase, pyroxene, and sometimes olivine, with Mohs hardness about 5–6 and no visible cleavage.
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Physical properties
Dark gray to black, smooth and rounded with a subdued glossy surface; basalt is typically composed of plagioclase, pyroxene, and sometimes olivine, with Mohs hardness about 5–6 and no visible cleavage.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near the surface; the pebble’s rounded shape suggests prolonged abrasion in a stream or on a beach. Its age cannot be determined from the image.
Uses & applications
Small pebbles are mainly used for decoration, crafts, and collecting; basalt also has construction and aggregate uses.
Geological facts
Basalt is one of Earth’s most abundant volcanic rocks and forms much of the ocean floor.
Field identification & locations
Look for a dense, dark, fine-grained rock without obvious crystals; water-worn basalt is common on volcanic coasts and in river gravels. A photo alone cannot confirm its composition.
