igneous
Basalt
Extrusive Igneous Rock (Mafic)
Hardness of 6 on the Mohs scale; dark gray to black color; dull to sub-to-glassy luster; fine-grained (aphanitic) crystal structure often with visible tiny vesicles; 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 to sub-to-glassy luster; fine-grained (aphanitic) crystal structure often with visible tiny vesicles; specific gravity around 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in iron and magnesium exposed at or very near the surface of a planet or moon, typically via volcanic eruptions.
Uses & applications
Used heavily in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in manufacturing insulation or stone wool.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins, and is also found abundantly on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight relative to its size, and fine-grained texture. Found worldwide in volcanic regions, oceanic islands, and large igneous provinces.
