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), glassy, or vesicular; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
Identified More igneous →
Explore Basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), glassy, or vesicular; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the Earth's surface, typically from volcanic eruptions. Geological age ranges from recent volcanic deposits to billions of years old.
Uses & applications
Used extensively in construction (crushed stone for road base, concrete aggregate), railroad ballast, and sometimes in manufacturing stone wool insulation or tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins, and it is also the primary volcanic rock found on the Moon and Mars.
Field identification & locations
Identify by its dark, fine-grained appearance, heavy weight, and common presence in volcanic regions. Often found in oceanic crust and major continental volcanic provinces (e.g., Columbia River Basalt Group).
