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 visible cleavage, and a 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 visible cleavage, and a 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 Earth's surface, often originating from volcanic eruptions.
Uses & applications
Commonly used 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 ocean basins, and it is also found extensively on the Moon and Mars.
Field identification & locations
Identified by its dark color, fine-grained texture, and heavy weight relative to its size. Commonly found in volcanic regions, ocean ridges, and flood basalt provinces worldwide.
