igneous
Basalt
Basalt
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing phenocrysts; Cleavage: None (conchoidal fracture); Specific gravity: 2.8-3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing phenocrysts; Cleavage: None (conchoidal fracture); Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. Most oceanic crust is basaltic.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. It can also be polished for use as floor tiles or monument stone.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up the majority of the ocean floor. It is also common on the Moon, Mars, and Venus.
Field identification & locations
Identified by its dark color, heavy weight (density), and fine-grained texture. It often shows tiny holes (vesicles) from gas bubbles. Commonly found in volcanic regions like Hawaii, the Pacific Northwest, and Iceland.
