igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0; Cleavage: None.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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 scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0; Cleavage: None.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (mafic lava) at or very near the Earth's surface. It can be found across all geological ages, notably in oceanic crust and large flood basalt provinces.
Uses & applications
Extensively used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as dimension stone and in the manufacturing of rock wool insulation.
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 common on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and very fine-grained texture where individual crystals are not visible to the naked eye. Found in volcanic regions and oceanic islands like Hawaii or Iceland.
