igneous
Vesicular basalt (possibly amygdaloidal basalt)
Basalt, chiefly plagioclase feldspar and pyroxene, with possible olivine and secondary mineral infillings
AI-generated identification · may be incorrectDark gray to black, fine-grained volcanic rock with irregular vesicles and pale mineral-filled cavities; typically dull to weakly glassy. Hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.8–3.0.
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Physical properties
Dark gray to black, fine-grained volcanic rock with irregular vesicles and pale mineral-filled cavities; typically dull to weakly glassy. Hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.8–3.0.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; cavities may later fill with zeolite, calcite, quartz, or chlorite. Basalt ranges from Precambrian to modern age and commonly forms lava flows and oceanic crust.
Uses & applications
Used as crushed aggregate, road stone, riprap, paving, and building stone; attractive amygdaloidal pieces are collected or cut for display.
Geological facts
The greenish material may be chlorite, epidote, or another alteration mineral, while pale patches may be feldspar or cavity fillings. A fresh streak is usually gray, and weak attraction to a magnet can occur if magnetite is abundant.
Field identification & locations
Identify it by its dark volcanic groundmass, scattered vesicles, and lack of visible large crystals; a steel scratch should usually mark it slightly. Common in volcanic terrains, especially Hawaii, Iceland, India, and oceanic crust exposures.
