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 vesicular with trapped gas bubbles containing mineral grains; 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 vesicular with trapped gas bubbles containing mineral grains; 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 Earth's surface, often from volcanic eruptions or oceanic rifts.
Uses & applications
Used in construction as crushed stone for road bases, railroad ballast, aggregate in concrete, and in manufacturing stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins and also forms significant volcanic structures on the Moon, Mars, and Venus.
Field identification & locations
Identified by its dark, fine-grained appearance, vesicular texture (holes from gas bubbles), and heavy feel relative to its size. Commonly found in volcanic regions worldwide.
