igneous
Basalt
Mafic extrusive igneous rock
Hardness of 6 on the Mohs scale, dark gray to black in color, dull to sub-metallic luster, aphanitic (fine-grained) crystal structure, specific gravity around 2.8 to 3.0
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black in color, dull to sub-metallic luster, aphanitic (fine-grained) crystal structure, specific gravity around 2.8 to 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 surface of a planet or moon, often associated with volcanic activity and oceanic crust formation
Uses & applications
Used extensively in construction as crushed aggregate for roads, railroad ballast, concrete production, and in the manufacturing of rock wool insulation
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's oceans, and it is also found abundantly on the Moon (forming the lunar maria) and Mars
Field identification & locations
Can be identified in the field by its dark color, fine-grained texture where individual crystals are generally not visible to the naked eye, and sometimes vesicular texture containing gas cavities
