igneous
Basalt
Basalt
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal 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
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal 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 exposed at or very near the surface of a terrestrial planet or a moon. Often found in oceanic crust and huge volcanic plateaus.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for paving and flooring.
Geological facts
Basalt is the most common rock type in the Earth's crust and also covers large areas of the Moon, Mars, and Venus. The Giant's Causeway in Northern Ireland is a famous example of columnar basalt.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture that lacks visible crystals to the naked eye. Commonly found in volcanic regions and ocean floor samples.
