igneous
Vesicular basalt pebble
Basalt, chiefly plagioclase feldspar, pyroxene, and iron-rich minerals
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to slightly vitreous, with small vesicles and possible weathering pits; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The rounded shape indicates water abrasion or deliberate tumbling.
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Physical properties
Dark gray to black, fine-grained, dull to slightly vitreous, with small vesicles and possible weathering pits; hardness about 5–6 Mohs, massive texture, and no obvious cleavage. The rounded shape indicates water abrasion or deliberate tumbling.
Formation & geological history
An extrusive volcanic rock formed when basaltic lava rapidly cooled at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes. Vesicles formed as gas bubbles escaped from the cooling lava; the specimen’s exact age cannot be determined visually.
Uses & applications
Commonly used as aggregate, road stone, riprap, landscaping rock, and sometimes as a polishing or massage stone. This small ordinary pebble has little commercial value.
Geological facts
The honeycomb-like pattern may reflect vesicles, weathering, or amygdales where cavities were partly filled by secondary minerals. Basalt is the most widespread volcanic rock on oceanic crust.
Field identification & locations
Identify it by its black fine-grained body, relatively high density, lack of visible large crystals, and bubble cavities; test with a steel knife for limited scratching and inspect a fresh break. Common along volcanic coasts, river gravels, and basalt provinces worldwide.
