igneous
Vesicular basalt (possibly weathered scoria)
Basaltic volcanic rock; chiefly plagioclase, clinopyroxene, and Fe–Mg oxides, with vesicles from trapped gas
AI-generated identification · may be incorrectDark gray to purplish, dull to slightly glassy, highly vesicular and irregularly weathered; hardness about 5–6, generally massive with no obvious cleavage, and specific gravity roughly 2.4–2.9 (lower if very porous).
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Physical properties
Dark gray to purplish, dull to slightly glassy, highly vesicular and irregularly weathered; hardness about 5–6, generally massive with no obvious cleavage, and specific gravity roughly 2.4–2.9 (lower if very porous).
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, leaving gas bubbles; likely Cenozoic or younger, though age cannot be determined from the photograph.
Uses & applications
Used as lightweight aggregate, landscaping stone, road material, and occasionally as a decorative or lapidary specimen; usually low jewelry value.
Geological facts
The rounded cavities are vesicles, not fossil holes; their surfaces may later develop secondary minerals such as zeolites, calcite, or silica.
Field identification & locations
Identify by its dark fine-grained matrix, abundant bubble cavities, relatively low density, and lack of sedimentary layering; common in volcanic fields, lava flows, and scoria cones worldwide. A fresh broken surface and streak/acid tests can refine identification.
