igneous
Vesicular basalt (possibly scoriaceous basalt)
Basalt, primarily plagioclase + pyroxene ± olivine; vesicles commonly lined or filled with secondary zeolites/calcite
AI-generated identification · may be incorrectDark gray to brown, fine-grained volcanic rock with abundant rounded gas cavities and a smoother weathered exterior; typically Mohs 5–6, dull to faintly vitreous luster, no visible cleavage, specific gravity about 2.7–3.0 (lower if highly vesicular).
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Physical properties
Dark gray to brown, fine-grained volcanic rock with abundant rounded gas cavities and a smoother weathered exterior; typically Mohs 5–6, dull to faintly vitreous luster, no visible cleavage, specific gravity about 2.7–3.0 (lower if highly vesicular).
Formation & geological history
Formed when basaltic lava erupted and rapidly cooled, trapping gas bubbles; likely Cenozoic or younger, though similar textures occur in older volcanic terrains.
Uses & applications
Used as lightweight aggregate, drainage stone, landscaping material, and occasionally as a decorative or teaching specimen; generally low commercial value.
Geological facts
The cavities are vesicles, not fossils; pale cavity fillings may be calcite, quartz, or zeolite minerals. The dense, smoothly weathered edge contrasts with the porous interior.
Field identification & locations
Identify by its black fine-grained matrix, magnetic response in many examples, and abundant vesicles; common in Hawaii, Iceland, oceanic islands, and volcanic regions worldwide. Acid testing can distinguish carbonate fillings, but avoid damaging collectible surfaces.
