igneous
Weathered basaltic rock
Basalt, chiefly plagioclase feldspar, clinopyroxene, and minor olivine or iron oxides
AI-generated identification · may be incorrectDark brown to gray, fine-grained and likely vesicular, with dull to slightly earthy luster; hardness about 5–6 Mohs, massive texture, no obvious cleavage, and specific gravity roughly 2.8–3.1.
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Physical properties
Dark brown to gray, fine-grained and likely vesicular, with dull to slightly earthy luster; hardness about 5–6 Mohs, massive texture, no obvious cleavage, and specific gravity roughly 2.8–3.1.
Formation & geological history
An extrusive igneous rock formed when mafic lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic or older volcanic activity; the brown surface reflects weathering and oxidation.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, riprap, and building stone; attractive dense pieces may be used decoratively, though this specimen has limited gem value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms lava flows, dikes, and volcanic plateaus.
Field identification & locations
Identify it by its dark color, fine grain, heavy feel, and inability to scratch with a copper coin; a steel knife may scratch some weathered surfaces. Common worldwide in volcanic regions, including Hawaii, Iceland, India, and the Pacific Northwest.
