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 tiny crystals (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 tiny crystals (phenocrysts) of olivine, pyroxene, or plagioclase. Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a planet or moon. It is the most common rock type in the Earth's oceanic crust.
Uses & applications
Used extensively in construction (crushed stone for road bases, concrete aggregate), railroad ballast, and in the production of basalt fiber for reinforced composites.
Geological facts
Basalt is the most abundant rock type on Earth's crust underlying the oceans, and it is also found in abundance on the Moon (making up the lunar maria) and Mars.
Field identification & locations
Identify in the field by its dark gray to black color, fine-grained texture, and high density. Commonly found in volcanic regions, shield volcanoes, and oceanic divergent boundaries.
