igneous
Basalt
Basalt (Mafic Extrusive Rock)
Hardness: 6 (Mohs); Color: dark grey to black or dark green; Luster: dull to earthy; Texture: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs)
- Color
- dark grey to black or dark green
- Luster
- dull to earthy
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Physical properties
Hardness: 6 (Mohs); Color: dark grey to black or dark green; Luster: dull to earthy; Texture: Aphanitic (fine-grained); 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 moon. Most examples are from the Cenozoic era, though it has formed throughout Earth's history.
Uses & applications
Widely used in construction for aggregate, road base, railroad ballast, and high-quality asphalt. It is also used in the manufacture of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in volcanic regions like the Pacific Northwest of the USA, Iceland, and Hawaii.
