igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic lava) at or very near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Extensively used in construction as crushed stone for road base, concrete aggregate, railroad ballast, and as a raw material for stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon, Venus, and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often breaks with a conchoidal or uneven fracture and lacks visible large crystals.
