igneous
Basalt
Extrusive igneous rock
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing small phenocrysts. Cleavage: None. Specific gravity: 2.8 to 3.0.
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing small phenocrysts. Cleavage: None. Specific gravity: 2.8 to 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the surface of a planet or moon. Geological age ranges from recent volcanic eruptions to billions of years old.
Uses & applications
Used in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the manufacturing of rock wool insulation and floor tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust, underlying more than 90% of all volcanic rock and making up most of the ocean floor as well as extensive continental flood basalt provinces.
Field identification & locations
Easily identified by its dark, fine-grained appearance, heavy weight, and often vesicular texture (containing gas cavities). Commonly found in volcanic regions worldwide, including oceanic islands and continental rift zones.
