igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0; Contains plagioclase feldspar, pyroxene, and olivine.
- Hardness
- 6 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0; Contains plagioclase feldspar, pyroxene, and olivine.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. It is the most common rock type in the Earth's crust, primarily making up the ocean floors.
Uses & applications
Extensively used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. It is also used in high-quality floor tiles and as a raw material for stone wool insulation.
Geological facts
Basalt is also found on other cellular bodies in our solar system, including the Moon, Mars, and Venus. On Earth, massive basalt flows known as Flood Basalts can cover thousands of square miles.
Field identification & locations
Identified in the field by its dark color, heavy weight (high density), and fine-grained texture. It often exhibits columnar jointing in large outcrops. Common in volcanic regions such as Iceland, Hawaii, and the Pacific Northwest.
