igneous
Basalt
Mafic extrusive igneous rock
Hardness of 6 on the Mohs scale, typically dark gray to black in color, dull to sub-withering luster, fine-grained aphanitic crystal structure, specific gravity around 2.8-3.0.
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Physical properties
Hardness of 6 on the Mohs scale, typically dark gray to black in color, dull to sub-withering luster, fine-grained aphanitic crystal structure, specific gravity around 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron exposed at or very near the surface of a planet or moon. Formed globally throughout geological time.
Uses & applications
Commonly used in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the production of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's oceanic crust and is also found abundantly on the Moon (forming the lunar maria) and Mars.
Field identification & locations
Identified by its dark color, fine-grained texture, and heavy weight relative to its size. Found extensively in volcanic regions worldwide.
