igneous
Basalt
Mafic extrusive igneous rock
AI-generated identification · may be incorrectHardness 6 on Mohs scale, dull/earthy luster, dark gray to black color, fine-grained (aphanitic) texture, specific gravity 2.8–3.0.
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Physical properties
Hardness 6 on Mohs scale, dull/earthy luster, dark gray to black color, fine-grained (aphanitic) texture, specific gravity 2.8–3.0.
Formation & geological history
Formed by the rapid cooling of low-viscosity, magnesium- and iron-rich basaltic lava at or near the Earth's surface.
Uses & applications
Extensively crushed for road base, concrete aggregate, railroad ballast, and dimension stone.
Geological facts
Basalt makes up over 90% of all volcanic rocks on Earth and is the primary constituent of oceanic crust and the lunar maria.
Field identification & locations
Identified by its fine grain, uniform dark color, and heavy weight relative to size. Ubiquitous in volcanic regions and gravel beds worldwide.
