igneous
Basalt
Extrusive mafic igneous rock
Hardness: 5-6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); 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. Found in oceanic crust and volcanic regions.
Uses & applications
Used in construction as crushed stone for road base, concrete aggregate, railroad ballast, and for high-temperature insulation in stone wool fibers.
Geological facts
Basalt is the most common rock type in Earth's crust and also makes up most of the surface of the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture with no visible crystals to the naked eye. Found worldwide in volcanic fields.
