igneous
Vesicular basalt (likely weathered volcanic rock)
Basalt, predominantly plagioclase + pyroxene ± olivine; approximate composition 45–52% SiO₂
AI-generated identification · may be incorrectGray-beige, fine-grained, dull to slightly glassy surface with small vesicles (gas cavities); typically hardness 5–6 Mohs, no visible cleavage, and specific gravity about 2.8–3.0. The specimen appears weathered and possibly coated with pale alteration minerals.
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Physical properties
Gray-beige, fine-grained, dull to slightly glassy surface with small vesicles (gas cavities); typically hardness 5–6 Mohs, no visible cleavage, and specific gravity about 2.8–3.0. The specimen appears weathered and possibly coated with pale alteration minerals.
Formation & geological history
An extrusive igneous rock formed when low-silica lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions from the Precambrian to the present. Vesicles formed as dissolved gases escaped from the cooling lava.
Uses & applications
Used widely as crushed aggregate, road base, railroad ballast, riprap, and building stone; attractive pieces may be collected or polished, though this small weathered specimen has limited commercial value.
Geological facts
Basalt makes up most of the oceanic crust and is the most abundant volcanic rock on Earth. Vesicle fillings may include calcite, zeolites, quartz, or secondary iron oxides.
Field identification & locations
Identify by its dark, fine-grained groundmass, heavy weight, and gas cavities; test with a steel knife and inspect for tiny interlocking crystals. Common in volcanic regions, oceanic islands, and ancient lava flows.
