igneous
Basalt
Mafic extrusive igneous rock
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-earthy. Crystal structure: Aphanitic (fine-grained), often containing small mineral phenocrysts of plagioclase feldspar and pyroxene. Cleavage: None. Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-earthy
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-earthy. Crystal structure: Aphanitic (fine-grained), often containing small mineral phenocrysts of plagioclase feldspar and pyroxene. Cleavage: None. Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava flows exposed at or very near the surface of a planet or moon. It is the most common rock type in the Earth's crust underlying the oceans.
Uses & applications
Used extensively in construction as crushed stone for road base, aggregate in concrete, railroad ballast, and in the production of stone wool insulation.
Geological facts
Basalt is not only the most common rock on Earth's oceanic crust, but it also makes up vast volcanic provinces on the Moon (the lunar maria) and constitutes a significant portion of the crusts of Mars and Venus.
Field identification & locations
Identified by its dark gray to black color, fine-grained (aphanitic) texture, and heavy feel relative to its size. Commonly found in volcanic regions, oceanic islands, and ancient flood basalt provinces worldwide.
