igneous
Basalt
Mafic volcanic rock (dominated by Plagioclase and Pyroxene)
Hardness: 6 on Mohs scale; Color: Dark grey, black, or dark greenish-brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey, black, or dark greenish-brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey, black, or dark greenish-brown; 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 low-viscosity magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most basalt on Earth is of Cenozoic to Archean age and forms most of the ocean floor.
Uses & applications
Used primarily in construction (crushed stone for road base and concrete), as high-quality railroad ballast, and for industrial stone-casting and fiber insulation (basalt wool).
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars, forming the dark 'seas' or maria visible on the lunar surface.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows a conchoidal or irregular fracture. Found in volcanic regions and ocean basins worldwide.
