igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing microscopic crystals of plagioclase feldspar and pyroxene; Cleavage: None; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing microscopic crystals 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 exposed at or very near the Earth's surface, typically at volcanic hotspots, oceanic rifts, and shield volcanoes.
Uses & applications
Widely used in construction as crushed stone for road bases, railroad ballast, and aggregate in concrete, as well as in the manufacture of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins and is also the most abundant volcanic rock on the terrestrial planets, including the dark maria regions of the Moon and the surface of Mars.
Field identification & locations
Can be identified in the field by its dark color, fine-grained texture, and heavy weight relative to its size. It is found worldwide in volcanic regions.
