igneous
Basalt
Basalt (extrusive igneous rock)
Hardness: 6-7 (Mohs); Color: Dark gray to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark gray to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of Earth. It is the most common volcanic rock.
Uses & applications
Extensively used in construction, especially as crushed stone for road base, railroad ballast, and concrete aggregate. Sometimes used in floor tiles and landscaping.
Geological facts
Basalt is common on Earth, but it is also the primary rock type on the Moon and Mars. On Earth, it forms the crust at the bottom of the oceans.
Field identification & locations
Identified by its dark color, high density, and fine-grained texture. It often weathers into a brownish-red color due to iron oxidation. Found in volcanic regions worldwide.
