igneous
Vesicular basalt
Basalt, likely amygdaloidal or scoriaceous basalt
AI-generated identification · may be incorrectDark gray to black, fine-grained volcanic rock with abundant irregular vesicles (gas cavities), dull to slightly glassy luster, and typical hardness about 5–6 Mohs. Cavities may contain weathering minerals or secondary zeolite/calcite coatings; exact composition cannot be confirmed visually.
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Physical properties
Dark gray to black, fine-grained volcanic rock with abundant irregular vesicles (gas cavities), dull to slightly glassy luster, and typical hardness about 5–6 Mohs. Cavities may contain weathering minerals or secondary zeolite/calcite coatings; exact composition cannot be confirmed visually.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping volcanic gases; commonly Cenozoic to modern, though basalt occurs throughout geologic time. The cavities formed during eruption and may later have been mineral-filled.
Uses & applications
Used as aggregate, road base, riprap, and occasionally decorative stone; attractive vesicular pieces are collected, though this specimen appears primarily of geological interest.
Geological facts
Its low-silica, iron- and magnesium-rich magma produces a dark color and relatively low viscosity lava. Vesicles distinguish it from dense basalt, while very abundant, frothy cavities can indicate scoria.
Field identification & locations
Identify by its dark fine-grained matrix, lightweight porous texture, and lack of large visible crystals; test for a glassy fracture and compare density. Common in volcanic regions such as Hawaii, Iceland, the Deccan Traps, and oceanic islands.
