igneous
Basalt
Extrusive igneous rock (Mafic)
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 of olivine, pyroxene, or plagioclase. Specific gravity: 2.8 - 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 of olivine, pyroxene, or plagioclase. Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava exposed at or very near the Earth's surface, commonly at divergent plate boundaries, oceanic hotspots, or flood basalt provinces.
Uses & applications
Used extensively in construction as crushed stone for road base, concrete aggregate, and railroad ballast, as well as in the production of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins and also makes up significant portions of the volcanic plains on the Moon and Mars.
Field identification & locations
Identified in the field by its dark, fine-grained groundmass, dense weight, and occasional vesicular (bubble-hole) textures. Found worldwide in volcanic regions.
