igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; 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
- 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 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; 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 exposed at or very near the surface of a terrestrial planet or a moon. Most basalt seafloor on Earth is less than 200 million years old, though continental flows can be much older.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for statues or polished as architectural veneer/slabs.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It also covers large areas of the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It is often found in volcanic regions, oceanic islands, and mid-ocean ridges.
