igneous
Likely basalt
Basalt; predominantly plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray-black, fine-grained, dull to slightly vitreous luster, with no visible crystals; hardness about 6–7 Mohs, massive texture, and typically no cleavage as a whole rock. The rough, dense appearance is consistent with basalt, though the image alone cannot confirm it.
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Physical properties
Dark gray-black, fine-grained, dull to slightly vitreous luster, with no visible crystals; hardness about 6–7 Mohs, massive texture, and typically no cleavage as a whole rock. The rough, dense appearance is consistent with basalt, though the image alone cannot confirm it.
Formation & geological history
An extrusive igneous rock formed when mafic lava rapidly cooled at or near Earth’s surface, commonly during volcanic eruptions; specimens may range from geologically recent to Precambrian in age.
Uses & applications
Widely used as crushed aggregate, road stone, railway ballast, riprap, and building stone; attractive polished varieties are used decoratively. Small unverified pieces generally have little commercial value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust, including the seafloor and many volcanic islands.
Field identification & locations
Identify it by its dense black-to-gray color, fine grain, high weight, and lack of obvious layering; a streak, magnetism, and hardness test can help distinguish it from slate, slag, or chert. Common locations include volcanic regions and oceanic crust.
