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), often containing phenocrysts. Specific gravity: 2.8 to 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 phenocrysts. Specific gravity: 2.8 to 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, mafic lava exposed at or very near the surface of a planet or moon.
Uses & applications
Used 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 crust underlying the ocean basins, and it is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark, fine-grained appearance, often with small visible mineral crystals like olivine or plagioclase. Found worldwide in volcanic provinces and oceanic ridges.
