igneous
Basalt
Basalt (Extrusive Mafic Igneous)
Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic), often crystalline but too small to see; Specific Gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic), often crystalline but too small to see; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the surface of a terrestrial planet or moon. Basalt comprises more than 90% of all volcanic rock on Earth.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Can also be used for decorative stone and stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the entirety of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identified by its dark color, heavy weight (relative to size), and fine-grained texture. It often breaks with a conchoidal fracture and lack of visible crystals.
