igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-vitreous; Structure: Fine-grained aphanitic with possible small phenocrysts; Cleavage: None; 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: Fine-grained aphanitic with possible small phenocrysts; 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 surface of a terrestrial planet or a moon. Most common rock in Earth's crust, primarily forming the ocean floors.
Uses & applications
Used in construction as aggregate, road base, and concrete; in landscaping; and occasionally polished for jewelry or decorative massage stones.
Geological facts
Basalt is a major constituent of the Martian and Lunar surfaces; the 'seas' on the Moon (Maria) are actually giant basaltic plains. It can also form unique hexagonal columns during cooling, such as at the Giant's Causeway.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and very small crystal grains that are difficult to see without a lens. Often found in volcanic regions or riverbeds near volcanic flows.
