igneous
Vesicular basalt (likely weathered lava rock)
Basalt; fine-grained mafic volcanic rock composed chiefly of plagioclase, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to black, dull to weakly glassy, with irregular vesicles and weathered cavities; hardness about 5–6 Mohs, no visible cleavage, fine-grained interlocking crystal structure, and specific gravity roughly 2.8–3.0.
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Physical properties
Dark gray to black, dull to weakly glassy, with irregular vesicles and weathered cavities; hardness about 5–6 Mohs, no visible cleavage, fine-grained interlocking crystal structure, and specific gravity roughly 2.8–3.0.
Formation & geological history
Forms when basaltic lava cools rapidly at or near Earth’s surface, trapping gas bubbles; specimens may range from modern flows to Precambrian volcanic rocks, depending on locality.
Uses & applications
Used as crushed aggregate, roadstone, riprap, ballast, and landscaping rock; attractive polished pieces are occasionally collected but are rarely used as gemstones.
Geological facts
The rounded shape and surface cavities suggest abrasion and weathering, possibly from a lava flow, beach, or river environment. A magnet may attract it weakly if it contains abundant magnetite.
Field identification & locations
Identify it by its dark color, fine texture, vesicles, and absence of sedimentary layering; distinguish it from slag by its natural mineral texture and lack of metallic glassy flow features. Common worldwide in volcanic regions, including Hawaii, Iceland, India, and the Pacific Northwest.
