igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-to-vitreous; Crystal structure: Aphanitic (fine-grained), often containing small crystals (phenocrysts) of plagioclase and pyroxene; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-to-vitreous
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Physical properties
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-to-vitreous; Crystal structure: Aphanitic (fine-grained), often containing small crystals (phenocrysts) of plagioclase and pyroxene; 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 Earth's surface, commonly at divergent plate boundaries, ocean islands, and continental flood basalt provinces.
Uses & applications
Widely used in construction as crushed stone for road bases, concrete aggregate, asphalt pavement, and in the production of basalt fiber.
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 the Devil's Postpile in California.
Field identification & locations
Identified by its dark, fine-grained appearance, heavy weight relative to size, and occasional vesicular texture (gas bubbles). Common globally in volcanic regions.
