igneous
Basalt
Basalt (mafic extrusive rock)
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to earthy
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron at or very near the Earth's surface. Common in oceanic crust and volcanic islands.
Uses & applications
Extensively used in construction as aggregate, road base, railroad ballast, and for high-durability floor tiles and pavers.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It also makes up the vast majority of 'seas' (maria) on the Moon.
Field identification & locations
Identified by its dark color, heavy weight for its size, and the lack of visible large crystals. Commonly found in coastal volcanic areas and riverbeds.
