igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark gray, black, or dark greenish; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal fracture); Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray, black, or dark greenish
- Luster
- Dull to sub-metallic
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray, black, or dark greenish; 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 at or very near the Earth's surface. Common in oceanic crust, mid-ocean ridges, and volcanic island arcs.
Uses & applications
Extensively used in construction for road base, concrete aggregate, and railroad ballast. Also used as floor tiles and in high-durability industrial applications.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found on the Moon and Mars, forming the dark 'seas' or maria.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. It often weathers to a reddish-brown color due to iron oxidation. Found worldwide in volcanic regions.
