igneous
Basalt
Mafic extrusive igneous rock
Hardness of 6 on the Mohs scale, dark gray to black color, dull to sub-woody luster, aphanitic (fine-grained) crystal structure, no visible cleavage, 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-woody luster, aphanitic (fine-grained) crystal structure, no visible cleavage, specific gravity around 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron exposed at or very near the surface of a planet or moon
Uses & applications
Commonly used in construction, aggregate for road bases, railroad ballast, and making stone wool insulation
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins and forms massive features like the Giant's Causeway in Northern Ireland
Field identification & locations
Found abundantly worldwide in volcanic regions, oceanic crust, and flood basalt provinces; identified by its dark, fine-grained appearance
