igneous
Vesicular basalt (possibly scoriaceous basalt)
Basalt; chiefly plagioclase, pyroxene, and olivine, with iron oxides
AI-generated identification · may be incorrectDark gray-green, fine-grained and very dense overall, with abundant rounded vesicles and lighter mineral-filled cavities; typically Mohs 5–6, dull to weakly vitreous, with no obvious cleavage. The pale spots may be calcite, zeolite, or weathered feldspar infillings.
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Physical properties
Dark gray-green, fine-grained and very dense overall, with abundant rounded vesicles and lighter mineral-filled cavities; typically Mohs 5–6, dull to weakly vitreous, with no obvious cleavage. The pale spots may be calcite, zeolite, or weathered feldspar infillings.
Formation & geological history
An extrusive volcanic rock formed when mafic lava rapidly cooled at or near the surface, commonly during the Cenozoic or younger volcanic activity. Vesicles formed from gas bubbles trapped in the cooling lava and later cavities may have been mineralized.
Uses & applications
Used as crushed aggregate, road stone, riprap, ballast, and dimension stone; attractive polished pieces are collected as volcanic specimens. Its jewelry value is generally low unless cavities contain notable zeolites or agate.
Geological facts
The rounded holes distinguish vesicular basalt from most massive basalt; mineral-filled holes produce amygdaloidal basalt. Exact identification would benefit from a fresh break, streak, magnetism test, and close examination of the cavity minerals.
Field identification & locations
Common in volcanic regions such as Iceland, Hawaii, the Pacific Northwest, India’s Deccan Traps, and oceanic crust. A hand lens, moderate magnetism, dark streak, and lack of acid reaction support basalt; strong fizz indicates carbonate infillings.
