igneous
Basalt
Extrusive igneous rock
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often contains microscopic or small crystals of plagioclase feldspar and pyroxene; Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often contains microscopic or small crystals of plagioclase feldspar and pyroxene; Cleavage: None; 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. Geological age ranges from recent volcanic activity to billions of years old.
Uses & applications
Used extensively in construction (crushed stone for road base, concrete aggregate), railroad ballast, and sometimes in manufacturing stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also the primary volcanic rock on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, fine-grained texture, and heavy weight. It is found worldwide in oceanic crusts, volcanic islands, and continental flood basalt provinces like the Columbia River Basalt Group.
