igneous
Vesicular basalt (weathered lava rock)
Basalt, a fine-grained mafic volcanic rock composed chiefly of plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectTypically dark gray to brown, fine-grained, dull to slightly vitreous, with irregular vesicles (gas cavities); hardness about 5–6 Mohs and no obvious cleavage. The rounded shape and brown surface indicate weathering and water abrasion.
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Physical properties
Typically dark gray to brown, fine-grained, dull to slightly vitreous, with irregular vesicles (gas cavities); hardness about 5–6 Mohs and no obvious cleavage. The rounded shape and brown surface indicate weathering and water abrasion.
Formation & geological history
Formed when basaltic lava rapidly cooled at or near Earth’s surface, trapping volcanic gas bubbles; its exact age and locality cannot be determined from the photograph. Such material commonly forms in oceanic crust, volcanic fields, and lava flows.
Uses & applications
Used widely as aggregate, roadstone, riprap, ballast, and landscaping rock; attractive pieces may be sold as natural curiosities, but this specimen has little gem or ornamental value.
Geological facts
The large cavity is a vesicle, possibly enlarged by weathering or mineral dissolution; small pale crystals may be feldspar or weathering products. It is not enough evidence for a meteorite, fossil, or pumice because it is relatively dense and only mildly vesicular.
Field identification & locations
Common in volcanic regions and stream or beach gravels; identify by its dense fine-grained texture, dark mafic color, and gas cavities. A streak, density test, and fresh broken surface would improve confirmation.
