igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing microscopic crystals or volcanic glass. Cleavage: None. Specific gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing microscopic crystals or volcanic glass. 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 from volcanic eruptions. Can be of various geological ages from Precambrian to recent active volcanism.
Uses & applications
Used extensively in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the manufacturing of rock wool insulation and tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins and also makes up extensive continental flood basalts like the Columbia River Plateau.
Field identification & locations
Identified in the field by its dark gray or black color, fine-grained texture, and high density. Commonly found in volcanic regions, oceanic islands, and ancient basaltic lava flows.
