igneous
Basalt
Extrusive igneous rock
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing phenocrysts; Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing phenocrysts; Cleavage: None; 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.
Uses & applications
Used in construction (crushed stone for road base, concrete aggregate), railroad ballast, and dimension stone.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's oceans, and it is also extensively found on the Moon and Mars.
Field identification & locations
Identify by its dark color, fine-grained texture, and heavy weight. Commonly found in volcanic regions, oceanic islands, and continental flood basalt provinces.
