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) to porphyritic; 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) to porphyritic; Cleavage: None; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Common in oceanic crust and large volcanic provinces.
Uses & applications
Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate; also used for high-quality floor tiles and stonework.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture that lacks visible crystals to the naked eye. Found worldwide in volcanic regions.
