igneous
Basalt
Mafic Extrusive Igneous Rock
Hardness: 6 on Mohs scale; Color: Dark grey to black, sometimes greenish; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black, sometimes greenish
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black, sometimes greenish; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for buildings or pavers.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars.
Field identification & locations
Identify by its characteristic dark color, heavy weight (relative to size), and very fine-grained texture that lacks visible crystals to the naked eye.
