igneous
Vesicular basalt (scoria-like basalt)
Basalt, predominantly plagioclase feldspar, pyroxene, and iron-titanium oxides
AI-generated identification · may be incorrectDark brown to black, fine-grained and strongly vesicular, with abundant rounded gas cavities and dull to subvitreous luster; hardness about 5–6 Mohs, no obvious cleavage, and specific gravity commonly 2.4–2.9 (lower when highly vesicular).
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Physical properties
Dark brown to black, fine-grained and strongly vesicular, with abundant rounded gas cavities and dull to subvitreous luster; hardness about 5–6 Mohs, no obvious cleavage, and specific gravity commonly 2.4–2.9 (lower when highly vesicular).
Formation & geological history
Formed when basaltic lava erupted and rapidly cooled while trapped volcanic gases expanded, producing vesicles; likely Cenozoic or younger, though similar textures occur in older volcanic rocks.
Uses & applications
Used as lightweight aggregate, drainage and landscaping stone, abrasive material, and occasionally in decorative or lapidary work; generally low jewelry value.
Geological facts
Its numerous holes distinguish it from dense basalt; unlike pumice, it is usually dark and commonly sinks in water because its vesicles are less abundant or less interconnected.
Field identification & locations
Identify it by its dark fine-grained matrix, abundant irregular pores, and relatively high density; common in volcanic regions, including Hawaii, Iceland, Japan, the Andes, and the Mediterranean. The rounded shape may reflect stream or beach transport.
