igneous
Basalt
Extrusive Igneous Rock (Mafic)
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), sometimes porphyritic; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), sometimes porphyritic; 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 surface of a planet or moon.
Uses & applications
Used extensively in construction (crushed stone for road bases, concrete aggregate), production of basalt fiber, and occasionally as dimension stone.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins and also makes up extensive volcanic formations on the Moon and Mars.
Field identification & locations
Identify by its dark, fine-grained appearance, heavy feel, and occasional tiny visible crystals (phenocrysts) of olivine or plagioclase.
