igneous
Basalt
Extrusive igneous rock
Hardness: 6 on Mohs scale. Color: Dark grey to black, sometimes weathering to brownish. Luster: Dull to sub-earthy. Crystal structure: Aphanitic (fine-grained), often containing phenocrysts of olivine, pyroxene, or plagioclase. Specific gravity: 2.8 - 3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black, sometimes weathering to brownish
- Luster
- Dull to sub-earthy
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Physical properties
Hardness: 6 on Mohs scale. Color: Dark grey to black, sometimes weathering to brownish. Luster: Dull to sub-earthy. Crystal structure: Aphanitic (fine-grained), often containing phenocrysts of olivine, pyroxene, or plagioclase. Specific gravity: 2.8 - 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. Geological age ranges from Precambrian to recent volcanic activity.
Uses & applications
Used extensively in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the production of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins. It is also found extensively on the Moon (forming the lunar maria) and Mars.
Field identification & locations
Identify in the field by its dark color, fine-grained texture, and high density. Commonly found in volcanic regions, oceanic islands, and continental flood basalt provinces.
