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 small mineral crystals like olivine, pyroxene, and plagioclase. 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 small mineral crystals like olivine, pyroxene, and plagioclase. Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron 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 as crushed stone for road bases, concrete aggregate, and railroad ballast, as well as in the manufacturing of rock wool insulation and floor tiles.
Geological facts
Basalt is not only the most common rock on Earth's crust, forming the bulk of ocean floors, but it is also abundantly found on the Moon (forming the lunar maria) and Mars.
Field identification & locations
Can be identified in the field by its dark color, heavy weight, and fine-grained texture. It is found worldwide in volcanic provinces, oceanic islands, and mid-ocean ridges.
