igneous
Basalt
Extrusive igneous rock
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing small phenocrysts of olivine, pyroxene, or plagioclase; Specific gravity: 2.8 to 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing small phenocrysts of olivine, pyroxene, or plagioclase; Specific gravity: 2.8 to 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in iron and magnesium exposed at or very near the surface of a planet or moon; widespread in oceanic crust and volcanic islands.
Uses & applications
Used in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the manufacturing of rock wool insulation and basalt fiber.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the oceans, and it is also found abundantly on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark, fine-grained, heavy appearance; commonly found near ancient or active volcanic regions, riverbeds, and as polished beach pebbles.
