igneous
Basalt
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black color, fine-grained (aphanitic) texture, dull to sub-metallic luster, 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 color, fine-grained (aphanitic) texture, dull to sub-metallic luster, 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.
Uses & applications
Used extensively in construction as crushed stone for road bases, concrete aggregate, and railroad ballast, as well as in manufacturing stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's oceanic crust and is also the primary rock making up the dark volcanic plains (maria) on the Moon and the surface of Mars.
Field identification & locations
Identified in the field by its dark color, fine-grained texture, and heavy weight. Commonly found in volcanic regions, oceanic islands, and continental flood basalt provinces.
