igneous
Basalt
Basalt (Extrusive Igneous Rock)
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained aphanitic; Cleavage: None; Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained aphanitic; 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 very near the Earth's surface during volcanic eruptions. It is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction for crushed stone, road base, concrete aggregate, and railroad ballast. High-quality dense basalt is sometimes used as dimension stone for tiles or monuments.
Geological facts
Basalt is not only the most common rock on Earth's surface but also makes up most of the ocean floors and is abundant on the Moon and Mars.
Field identification & locations
Identify by its characteristic dark color, heavy weight (relative to size), and very fine-grained texture. Often found in volcanic regions or as 'river rocks' transported from volcanic Highlands.
