igneous
Basalt
Mafic Volcanic Rock
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None/Irregular
- Hardness
- 6 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None/Irregular
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 volcanic islands.
Uses & applications
Used in construction as a road base, concrete aggregate, and railroad ballast. Also used as dimension stone and in high-temperature insulation (basalt fiber).
Geological facts
Basalt is the most common rock type in the Earth's crust and also covers large areas of the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and lack of visible crystals to the naked eye. Found worldwide in volcanic regions.
