igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black, often weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8-3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black, often weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black, often weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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 a terrestrial planet or a moon. Most common rock type in the Earth's crust.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used in stone carvings and as a thermal insulator.
Geological facts
Basalt is the most common rock on Earth's surface 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, and fine-grained texture. It often shows vesiculation (small holes from gas bubbles). Common in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.
