igneous
Basalt
Basalt (Mafic Volcanic Rock)
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; 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 near the surface of a terrestrial planet or moon. Most ocean basins are composed of basalt.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality paving stones. Some dense varieties are used for sculpture.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars. It can form column-like structures when cooling, such as the Giant's Causeway.
Field identification & locations
Identified in the field by its dark color, heavy weight (density), and fine-grained texture. It often lacks visible crystals to the naked eye.
