igneous
Basalt
Mafic extrusive igneous rock
Hardness: 6 on Mohs scale; Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), sometimes porphyritic or vesicular; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), sometimes porphyritic or vesicular; 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. Geologically widespread across Earth's oceanic crust and volcanic islands.
Uses & applications
Used extensively in construction as crushed stone for road bases, concrete aggregate, and railroad ballast, as well as in the production of basalt fiber.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the oceanic floor and large volcanic provinces like the Deccan Traps. It is also the primary volcanic rock found on the Moon and Mars.
Field identification & locations
Easily identified by its dark, fine-grained groundmass, often with visible small crystals of plagioclase feldspar, pyroxene, or olivine. Found globally in volcanic regions, rift zones, and ocean ridges.
