igneous
Weathered vesicular volcanic rock
Likely basaltic andesite or scoriaceous basalt; exact identification requires fresh surface and testing
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to weakly earthy luster with rounded weathering and small vesicles; likely hardness about 5–6 Mohs, massive texture, no obvious cleavage, and specific gravity roughly 2.6–2.9.
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Physical properties
Dark gray-brown, fine-grained, dull to weakly earthy luster with rounded weathering and small vesicles; likely hardness about 5–6 Mohs, massive texture, no obvious cleavage, and specific gravity roughly 2.6–2.9.
Formation & geological history
An extrusive igneous rock formed when mafic lava cooled at or near the surface, trapping gas bubbles; probably geologically young relative to continental basement, though the photograph cannot establish age.
Uses & applications
Common basalt is used as crushed aggregate, road stone, riprap, and occasionally building stone; this weathered specimen has mainly educational or modest collecting value.
Geological facts
The cavities are vesicles, formed by escaping volcanic gases, and the greenish patches may represent secondary alteration minerals such as chlorite or epidote.
Field identification & locations
Look for a fine crystalline groundmass, vesicles, and a heavy, dense feel; a fresh broken surface, streak, magnet test, and hardness test help distinguish basalt from weathered sandstone or slag. Common worldwide in volcanic regions, including Hawaii, Iceland, and continental lava fields.
