igneous
Vesicular basalt pebble
Basalt, predominantly plagioclase–pyroxene–olivine
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to slightly vitreous; numerous small vesicles and possible weathered olivine grains. Hardness about 6–7 Mohs, massive texture, no obvious cleavage, specific gravity roughly 2.8–3.0.
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Physical properties
Dark gray-brown, fine-grained, dull to slightly vitreous; numerous small vesicles and possible weathered olivine grains. Hardness about 6–7 Mohs, massive texture, no obvious cleavage, specific gravity roughly 2.8–3.0.
Formation & geological history
An extrusive mafic igneous rock formed when low-silica lava cooled rapidly at or near Earth’s surface, trapping gas bubbles. Its exact age cannot be determined from the image; it may be a relatively young beach or river cobble.
Uses & applications
Used as aggregate, road base, riprap, landscaping stone, and occasionally lapidary material; ordinary pebbles have little jewelry value.
Geological facts
Basalt is the most common volcanic rock and forms much of oceanic crust and many volcanic islands. Vesicles indicate gas-rich lava, while the rounded shape reflects transport and abrasion.
Field identification & locations
Identify it by its dark color, fine texture, toughness, and scattered holes; a streak, magnet test, and fresh broken surface can help distinguish it from scoria or weathered andesite. Common in volcanic regions, riverbeds, and beaches.
