igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-vitreous; Structure: Aphanitic (fine-grained), often vesicular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-vitreous; Structure: Aphanitic (fine-grained), often vesicular; Cleavage: None (conchoidal fracture); 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 surface of a terrestrial planet or a moon. Common in oceanic crust and volcanic islands.
Uses & applications
Used primarily in construction for road base, concrete aggregate, railroad ballast, and dimension stone for paving or sculptures.
Geological facts
Basalt is the most common rock type in the Earth's crust and also covers large portions of the surfaces of Mars and Venus. The Lunar Maria are also composed largely of basalt.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. Found globally in volcanic regions like Hawaii, Iceland, and the Columbia River Plateau.
