igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 5-6 (Mohs); Color: Dark gray, black, or dark greenish-gray; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark gray, black, or dark greenish-gray
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark gray, black, or dark greenish-gray; Luster: Dull to sub-metallic; 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 at or very near the Earth's surface. Common in oceanic crust and mid-ocean ridges.
Uses & applications
Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate. High-density varieties are used in sea walls.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floors. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identified by its dark color, heavy weight (density), and fine-grained texture where individual crystals are too small to see with the naked eye. Found worldwide in volcanic regions.
