igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 on Mohs scale; Color: Dark grey to black, weathering to brownish-green; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal fracture); Specific gravity: 2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black, weathering to brownish-green
- 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 Mohs scale; Color: Dark grey to black, weathering to brownish-green; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal fracture); Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. It is the most common volcanic rock on Earth and makes up most of the ocean floor.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for floor tiles or monuments.
Geological facts
Basalt is also found on the Moon, Mars, and Venus. The 'Maria' on the lower parts of the Moon are actually vast basaltic plains. It can form unique geometric columns like those at the Giant's Causeway.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible large crystals. Commonly found in volcanic regions, oceanic islands (like Hawaii), and large igneous provinces.
