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. 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. Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron exposed at or very near the Earth's surface, typically associated with volcanic eruptions and oceanic crust formation.
Uses & applications
Used in construction as crushed stone for road base, aggregate in concrete, railroad ballast, and in the production of basalt fiber.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also found abundantly on the Moon and Mars.
Field identification & locations
Identify in the field by its dark, dense, fine-grained appearance, often showing vesicular (gas bubble) textures. Found worldwide in volcanic regions.
