igneous
Basalt
Mafic extrusive igneous rock
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing microscopic or very small crystals. Specific gravity: 2.8 - 3.0.
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-vitreous
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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), often containing microscopic or very small crystals. Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava exposed at or very near the surface of a planet or moon. Ages vary widely from recent volcanic eruptions to billions of years old.
Uses & applications
Used extensively in construction (crushed rock for road base, concrete aggregate), railroad ballast, and sometimes for producing stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the oceans and forms most of the volcanic islands on Earth. It is also the most common rock type on the surfaces of the inner planets and Earth's moon.
Field identification & locations
Identify in the field by its dark, fine-grained, heavy appearance. It is found worldwide in volcanic provinces, oceanic crusts, and ancient lava plateaus.
