igneous
Vesicular basalt (likely weathered basaltic rock)
Basalt; predominantly plagioclase, clinopyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to weakly lustered, with numerous small vesicles and tan/orange weathering or mineral infill; hardness about 5–6, generally massive with no obvious cleavage, specific gravity roughly 2.7–3.0.
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Physical properties
Dark gray to black, fine-grained, dull to weakly lustered, with numerous small vesicles and tan/orange weathering or mineral infill; hardness about 5–6, generally massive with no obvious cleavage, specific gravity roughly 2.7–3.0.
Formation & geological history
An extrusive igneous rock formed when low-silica basaltic lava cooled rapidly at or near Earth’s surface; age cannot be determined from the photograph and may range from recent to Precambrian.
Uses & applications
Used as aggregate, road base, riprap, landscaping stone, and occasionally ornamental material; usually low collector value unless provenance or unusual vesicle fillings are significant.
Geological facts
The rounded shape may reflect stream or shoreline abrasion rather than original lava morphology. Pale spots could be feldspar, zeolite, calcite, or weathering products, but testing is needed for identification.
Field identification & locations
Identify by its dark fine-grained groundmass, heavy weight, lack of visible quartz, and vesicles; common in volcanic regions worldwide, including Hawaii, Iceland, the western Americas, and oceanic islands. A streak, magnetism test, fresh break, and acid test can refine identification.
