igneous
Vesicular basalt (possibly scoriaceous basalt)
Basalt, chiefly plagioclase feldspar, clinopyroxene, and iron-titanium oxides
AI-generated identification · may be incorrectDark gray, fine-grained volcanic rock with abundant rounded gas vesicles, weathered brown surfaces, and scattered pale mineral grains; typically Mohs 5–6, dull to slightly vitreous luster, and no obvious cleavage. The light spots may be feldspar or secondary zeolite/calcite fillings.
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Physical properties
Dark gray, fine-grained volcanic rock with abundant rounded gas vesicles, weathered brown surfaces, and scattered pale mineral grains; typically Mohs 5–6, dull to slightly vitreous luster, and no obvious cleavage. The light spots may be feldspar or secondary zeolite/calcite fillings.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping volcanic gases; likely Cenozoic or younger, though age cannot be determined from the photograph. Common in lava flows, scoria cones, and volcanic islands.
Uses & applications
Used as crushed aggregate, road stone, riprap, and occasionally decorative stone; vesicular specimens are mainly collected as geological examples.
Geological facts
Vesicles distinguish it from dense basalt and many sedimentary rocks; mineral-filled vesicles indicate later groundwater alteration. It may be informally called amygdaloidal basalt if the cavities are filled.
Field identification & locations
Common worldwide in volcanic regions, including Hawaii, Iceland, the Pacific Northwest, India, and oceanic crust. Confirm with a fresh dark-gray fracture, glassy volcanic texture, and lack of visible sedimentary layering; a white streak or strong acid reaction would suggest calcite infill.
