igneous
Basalt
Extrusive Igneous Rock
Hardness: 5-6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing microscopic crystals or glass. Specific gravity: 2.8-3.0.
- Hardness
- 5-6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing microscopic crystals or glass. Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a planet or moon. Geological age ranges from Precambrian to recent volcanic activity.
Uses & applications
Used extensively in construction as crushed stone for road bases, concrete aggregate, and railroad ballast, as well as in the production of rock wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's oceans and forms famous geological formations like the Giant's Causeway in Northern Ireland and Devils Postpile in California. It is also the most common volcanic rock on the Moon and Mars.
Field identification & locations
Can be identified in the field by its dark color, fine-grained or aphanitic texture, and heavy weight relative to its size. Found worldwide in volcanic provinces, oceanic crusts, and flood basalt plateaus.
