igneous
Basalt
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, conchoidal to uneven fracture, specific gravity around 2.8 - 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, conchoidal to uneven fracture, specific gravity around 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, often through volcanic eruptions.
Uses & applications
Used extensively 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 world's ocean basins, and it is also abundantly found on the Moon, Mars, and Venus.
Field identification & locations
Identified by its dark color and fine-grained texture where individual crystals are typically too small to see with the naked eye, sometimes showing vesicular (gas bubble) cavities.
