igneous
Basalt
Extrusive volcanic basalt
Hardness: 6 (Mohs); Color: Dark gray to black, often weathering to brown; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0.
- Hardness
- 6 (Mohs)
- Color
- Dark gray to black, often weathering to brown
- Luster
- Dull/Earthy
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 (Mohs); Color: Dark gray to black, often weathering to brown; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the surface of a planet or moon; most of the Earth's oceanic crust is composed of basalt.
Uses & applications
Used primarily in construction for crushed stone, aggregate in concrete and asphalt, and occasionally for high-durability floor tiles or monuments.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up the lunar maria on the Moon. It frequently forms distinctive columnar joints when cooling.
Field identification & locations
Identify by its heavy weight (high density), dark color, and very fine grains that are difficult to see with the naked eye. Commonly found in volcanic regions and along oceanic ridges.
