igneous
Basalt
Basalt
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to submetallic; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0; Cleavage: None.
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull to submetallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to submetallic; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0; Cleavage: None.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most of the Earth's oceanic crust is composed of basalt.
Uses & applications
Widely used in construction as aggregate, for road base, concrete, and asphalt; also used in stone carving and as thermal insulation in the form of rock wool.
Geological facts
Basalt is the most common rock type in the Earth's crust. It also covers large areas of the Moon (the Lunar Maria), Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.
