igneous
Basalt
Extrusive Igneous Rock (Mafic)
Hardness: 6 on the Mohs scale. Color: Dark gray to black, sometimes greenish due to weathering. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often with vesicular texture containing holes (vugs) left by escaping gas bubbles. Specific gravity: 2.8-3.0.
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black, sometimes greenish due to weathering
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black, sometimes greenish due to weathering. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often with vesicular texture containing holes (vugs) left by escaping gas bubbles. Specific gravity: 2.8-3.0.
Formation & geological history
Formed by the rapid cooling of low-viscosity, magnesium- and iron-rich (mafic) lava exposed at or very near the Earth's surface, often from volcanic eruptions or mid-ocean ridges.
Uses & applications
Used in construction as crushed stone for road bases, 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 world's oceans and forms famous geological formations like the Giant's Causeway in Northern Ireland and Devils Postpile in California.
Field identification & locations
Easily identified by its dark color, fine-grained texture, and frequently vesicular nature (holes from gas bubbles). Often found on beaches or volcanic regions worldwide.
