igneous
Basalt
Basalt
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained); Cleavage: None/conchoidal; Specific Gravity: 2.8–3.0.
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained); Cleavage: None/conchoidal; Specific Gravity: 2.8–3.0.
Formation & geological history
Formed by the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most common rock in Earth's crust.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for fiber manufacture (basalt fiber) and as a building stone.
Geological facts
Basalt is the most common volcanic rock on Earth and also makes up a large portion of the crust of the Moon, Venus, and Mars. The giant columns of the Giant's Causeway in Ireland are made of basalt.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture with tiny visible crystals. Common in volcanic regions and ocean floor samples.
