igneous
Basalt
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black color, dull luster, aphanitic (fine-grained) crystal structure, specific gravity around 2.8-3.0.
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black color, dull luster, aphanitic (fine-grained) 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.
Uses & applications
Widely used in construction, as crushed stone in road base, railroad ballast, aggregate in asphalt, and in the production of rock wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's oceans, and it is also abundantly found on the Moon and Mars.
Field identification & locations
Easily identified by its dark, fine-grained appearance. Found globally in volcanic provinces, oceanic crusts, and flood basalt regions.
