igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale, Color: Dark gray to black, Luster: Dull to sub-vitreous, Crystal structure: Aphanitic (fine-grained), dense microcrystalline texture, Specific gravity: 2.8 - 3.0
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Physical properties
Hardness: 6 on the Mohs scale, Color: Dark gray to black, Luster: Dull to sub-vitreous, Crystal structure: Aphanitic (fine-grained), dense microcrystalline texture, Specific gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a planet or moon, typically through volcanic eruptions.
Uses & applications
Used extensively in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the production of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also the predominant volcanic rock on the Moon, Mars, and Venus.
Field identification & locations
Can be identified in the field by its dark color, fine-grained aphanitic texture where individual crystals are not visible to the naked eye, and sometimes vesicular structure from trapped gas bubbles.
