igneous
Weathered basalt (possibly vesicular basalt)
Basalt; predominantly plagioclase, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to weakly vitreous, with weathered rusty-brown surfaces and small vesicles or cavities. Hardness about 6 Mohs; massive texture and no obvious cleavage.
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Physical properties
Dark gray to black, fine-grained, dull to weakly vitreous, with weathered rusty-brown surfaces and small vesicles or cavities. Hardness about 6 Mohs; massive texture and no obvious cleavage.
Formation & geological history
An extrusive mafic igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface. The specimen’s age cannot be determined from the image; basalt forms from Precambrian to modern volcanic activity.
Uses & applications
Widely used as crushed aggregate, road stone, railway ballast, riprap, and occasionally dimension stone. Common specimens have little jewelry value.
Geological facts
The pale brown and whitish areas likely represent weathering, oxidation, or secondary minerals filling vesicles. Some cavities may be lined with zeolite, calcite, or silica, but this cannot be confirmed visually.
Field identification & locations
Common in volcanic regions, oceanic crust, flood-basalt provinces, and river gravels. Identify by its heavy, dark fine-grained body, lack of obvious layering, and possible gas bubbles; a fresh broken surface and streak or hardness tests improve confidence.
