igneous
Rounded vesicular basalt pebble
Basalt, typically plagioclase + clinopyroxene ± olivine, with vesicles
AI-generated identification · may be incorrectFine-grained, gray-brown, dull to slightly vitreous surface with numerous small holes; hardness about 5–6 Mohs, no visible cleavage, and specific gravity commonly 2.7–3.0. The rounded shape indicates water abrasion or tumbling.
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Physical properties
Fine-grained, gray-brown, dull to slightly vitreous surface with numerous small holes; hardness about 5–6 Mohs, no visible cleavage, and specific gravity commonly 2.7–3.0. The rounded shape indicates water abrasion or tumbling.
Formation & geological history
An extrusive volcanic rock formed when mafic lava cooled rapidly at or near Earth’s surface, likely in the Cenozoic or younger depending on locality. Vesicles formed from gas bubbles trapped during solidification; the image alone cannot establish age or exact composition.
Uses & applications
Commonly used as aggregate, road stone, landscaping material, and sometimes abrasive media; attractive pieces may be sold as natural beach or river pebbles. Collector value is usually minimal.
Geological facts
Basalt is Earth’s most abundant volcanic rock and makes up much of the oceanic crust. Its vesicles may later become filled with secondary minerals such as zeolites, calcite, or silica.
Field identification & locations
Identify it by its dark fine-grained matrix, heavy feel, and gas-bubble cavities; it is unlike lightweight pumice because it is denser and less glassy. Common in volcanic regions, river beds, beaches, and glacial deposits worldwide.
