igneous
Weathered basalt (possibly vesicular basalt)
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to brown, fine-grained, dull to weakly submetallic where weathered, with rounded vesicular or irregular surfaces. Hardness about 5–6 Mohs; no obvious cleavage; dense, though vesicles may reduce specific gravity to roughly 2.7–3.0.
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Physical properties
Dark gray to brown, fine-grained, dull to weakly submetallic where weathered, with rounded vesicular or irregular surfaces. Hardness about 5–6 Mohs; no obvious cleavage; dense, though vesicles may reduce specific gravity to roughly 2.7–3.0.
Formation & geological history
An extrusive volcanic rock formed when mafic lava cooled rapidly at or near Earth’s surface; its age cannot be determined from the photograph and may range from recent to billions of years.
Uses & applications
Used as crushed aggregate, road base, railway ballast, riprap, building stone, and occasionally as a decorative or lapidary material.
Geological facts
Basalt is the most widespread volcanic rock on Earth and forms much of the oceanic crust. Brown coloration and rounded relief likely reflect oxidation and prolonged weathering.
Field identification & locations
Look for a dark, compact, fine-grained texture, very high density, and possible tiny vesicles; a streak, fresh broken surface, and magnet test help distinguish it from weathered slag or other dark rocks. Common worldwide, especially volcanic regions and oceanic islands.
