igneous
Basalt
Mafic Fine-Grained Igneous Rock
Hardness: 6 on Mohs scale; Color: Dark grey to black or brownish-grey; Luster: Earthy, dull; Structure: Aphanitic (fine-grained), dense; Cleavage: None; Specific gravity: 2.8-3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black or brownish-grey
- Luster
- Earthy, dull
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black or brownish-grey; Luster: Earthy, dull; Structure: Aphanitic (fine-grained), dense; Cleavage: None; 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. Commonly associated with oceanic crust, volcanic islands, and flood basalt provinces.
Uses & applications
Widely used as crushed stone for road base, concrete aggregate, railway ballast, dimension stone, and cast basalt wear-resistant tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up almost all of the ocean floors. It is also extremely common on the Moon and Mars.
Field identification & locations
Look for a dark, heavy, fine-grained rock with no visible large crystals (unless porphyritic with olivine or plagioclase phenocrysts). Extremely widespread near volcanic regions.
