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 tiny plagioclase feldspar and pyroxene phenocrysts. Cleavage: None. 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 tiny plagioclase feldspar and pyroxene phenocrysts. Cleavage: None. Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, iron- and magnesium-rich lava exposed at or very near the surface of a planet or moon. It is the most common rock type in the Earth's oceanic crust.
Uses & applications
Used extensively in construction (crushed stone for road base, concrete aggregate), railroad ballast, and sometimes in the manufacture of stone wool insulation.
Geological facts
Basalt is the most common rock type of Earth's crust underlying the ocean basins, and it is also found abundantly on the Moon, Mars, and Venus.
Field identification & locations
Can be identified in the field by its dark gray to black color, fine-grained texture, and heavy feel. Common worldwide in volcanic regions, oceanic islands, and flood basalt provinces.
