igneous
Dark mafic rock, likely basalt
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine or iron oxides
AI-generated identification · may be incorrectFine-grained, dark gray to brown, dull to weakly vitreous luster; hardness about 5–6, generally massive with no obvious cleavage. The image is insufficient to confirm texture or density.
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Physical properties
Fine-grained, dark gray to brown, dull to weakly vitreous luster; hardness about 5–6, generally massive with no obvious cleavage. The image is insufficient to confirm texture or density.
Formation & geological history
Extrusive igneous rock formed when mafic lava cooled rapidly at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, building stone, and occasionally decorative material; ordinary pieces have little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust, including seafloor and many volcanic islands.
Field identification & locations
Identify by its dark color, heavy feel, fine texture, and lack of visible large crystals; magnetic response may occur from iron oxides. Common worldwide in volcanic regions and oceanic crust.
