igneous
Basalt
Mafic extrusive igneous rock
Hardness of 6 on the Mohs scale, dark gray to black color, dull to sub-with glassy or fine-grained aphanitic texture, 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-with glassy or fine-grained aphanitic texture, 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 Earth's surface, often originating from volcanic eruptions.
Uses & applications
Used extensively in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the production of basalt fiber.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's oceans and also makes up extensive volcanic plains on the Moon and Mars.
Field identification & locations
Can be identified in the field by its dark, fine-grained appearance, heavy weight relative to size, and association with volcanic terrains.
