igneous
Basalt
Mafic extrusive igneous rock
Hardness of 6 on the Mohs scale, typically dark gray to black in color, dull to sub-with a fine-grained aphanitic crystal structure, no prominent cleavage, and a relatively high 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-with a fine-grained aphanitic crystal structure, no prominent cleavage, and a relatively high specific gravity around 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava exposed at or very near the surface of a planet or moon. It is the most common rock type in the Earth's oceanic crust.
Uses & applications
Used heavily 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 volcanic rock on Earth and also makes up the vast majority of the lunar maria and the surface crust of Venus and Mars.
Field identification & locations
Can be identified in the field by its dark, fine-grained appearance, often forming columnar jointing in large deposits. Found worldwide in volcanic regions and oceanic ridges.
