igneous
Basalt
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, typically dark gray to black in color, fine-grained (aphanitic) texture, dull to sub-vitreous luster, and specific gravity around 2.8 to 3.0.
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Physical properties
Hardness of 6 on the Mohs scale, typically dark gray to black in color, fine-grained (aphanitic) texture, dull to sub-vitreous luster, and specific gravity around 2.8 to 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 Earth's surface, often originating from volcanic eruptions.
Uses & applications
Used widely in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the manufacturing of fiberglass and stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins and is also found abundantly on the Moon, Mars, and Venus.
Field identification & locations
Can be identified in the field by its dark color, heavy weight, and fine-grained texture; very common in volcanic regions and glacial till derived from northern shields.
