igneous
Dark volcanic rock, likely basalt
Basalt; mainly plagioclase feldspar, pyroxene, and minor olivine or iron oxides
AI-generated identification · may be incorrectFine- to medium-grained, dark gray to black, generally dull to weakly vitreous, with scattered pale feldspar crystals and possible vesicles; hardness about 6–7 Mohs, no prominent cleavage as a rock, density roughly 2.8–3.0 g/cm³.
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Physical properties
Fine- to medium-grained, dark gray to black, generally dull to weakly vitreous, with scattered pale feldspar crystals and possible vesicles; hardness about 6–7 Mohs, no prominent cleavage as a rock, density roughly 2.8–3.0 g/cm³.
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 rounded shape appears natural or weathered, though the surface may have been polished or worn.
Uses & applications
Used as crushed aggregate, road base, railway ballast, riprap, paving stone, and occasionally decorative stone; common specimens have little commercial collector value.
Geological facts
Basalt is Earth’s most abundant volcanic rock and forms much of the oceanic crust. Pale crystals are likely plagioclase phenocrysts, while vesicles indicate gas-rich lava.
Field identification & locations
Identify it by its black, heavy, fine-grained mafic texture, pale feldspar flecks, and lack of obvious layering; common worldwide in volcanic regions, including Hawaii, Iceland, India, and the Pacific Northwest.
