igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; 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. Common in oceanic crust and volcanic regions.
Uses & applications
Used primarily in construction for road base, concrete aggregate, railroad ballast, and high-quality floor tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and very fine grains that are hard to see without a lens. Often found in volcanic fields.
