igneous
Basalt
Basalt
Hardness: 6 (Mohs); Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black, weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black, 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 in the Earth's crust, primarily forming the ocean floor.
Uses & applications
Extensively used in construction for aggregate in concrete, asphalt paving, road base, and railroad ballast. High-quality specimens are used in stone masonry and statues.
Geological facts
Basalt is the most common rock type on the surfaces of the inner planets, including Mars and the Moon (the dark lunar Maria are basaltic plains). It often forms unique columnar jointing patterns like the Giant's Causeway.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows a brownish weathered crust (as seen in the image). Found in volcanic regions and oceanic crust.
