igneous
Basalt
Basalt (Aphanitic Mafic Volcanic Rock)
Hardness: 6 on Mohs scale; Color: typically dark grey to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; Specific gravity: 2.8 - 3.0 (dense).
- Hardness
- 6 on Mohs scale
- Color
- typically dark grey to black
- Luster
- dull to 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 on Mohs scale; Color: typically dark grey to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; Specific gravity: 2.8 - 3.0 (dense).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface of a terrestrial planet or a moon. Most basalt flows are from the Cenozoic era, though it has formed throughout Earth's history.
Uses & applications
Extensively used in construction as an aggregate (crushed stone) for road bases, concrete, and railroad ballast. In industry, it is used for high-tensile basalt fibers and as 'cast basalt' for wear-resistant liners.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars (the dark plains on the Moon, known as Maria, are basaltic).
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture with no visible crystals to the naked eye. Found worldwide in volcanic regions, such as the Giant's Causeway or the Hawaiian Islands.
