igneous
Basalt
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, typically dark gray to black in color, aphanitic (fine-grained) to glassy crystal structure, dull to sub-metallic luster, no distinct cleavage, and specific gravity ranging from 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, aphanitic (fine-grained) to glassy crystal structure, dull to sub-metallic luster, no distinct cleavage, and specific gravity ranging from 2.8 to 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.
Uses & applications
Used extensively in construction (crushed stone for road bases, concrete aggregate), railroad ballast, and sometimes in manufacturing stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins, and it also forms massive volcanic structures like the Giant's Causeway in Northern Ireland and the Columbia River Plateaus.
Field identification & locations
Can be identified in the field by its dark, fine-grained appearance, often vesicular (containing gas bubbles), and heavy weight relative to its size. Commonly found in volcanic regions worldwide.
