igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-to-vitreous. Crystal structure: Aphanitic (fine-grained), sometimes porphyritic. Cleavage: None. Specific gravity: 2.8 - 3.0.
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-to-vitreous
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-to-vitreous. Crystal structure: Aphanitic (fine-grained), sometimes porphyritic. 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 Precambrian to recent volcanic activity.
Uses & applications
Used in construction as crushed stone for road base, concrete aggregate, railroad ballast, and in the production of rock wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also abundantly found on the Moon (forming the lunar maria) and Mars.
Field identification & locations
Identify by its dark, fine-grained appearance, dense weight, and occasional vesicular (bubble-hole) textures. Found worldwide in volcanic regions, oceanic islands, and continental flood basalt provinces.
