igneous
Basalt
Basalt (Mafic Extrusive)
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull/earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None/clastic; Specific gravity: 2.8 - 3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull/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: Dark grey to black; Luster: Dull/earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None/clastic; Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (mafic) exposed at or very near the surface of a terrestrial planet or a moon. Most basalt flows are from the Cenozoic era, though it can date back billions of years.
Uses & applications
Used primarily in construction for crushed stone, road base, concrete aggregate, and railroad ballast. High-quality dense basalt is also used for floor tiles and architectural veneers.
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 on the Moon, Mars, and Venus in large quantities.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture lacking visible crystals. Commonly found in volcanic fields, ocean ridges, and flood basalt provinces like the Deccan Traps or Columbia River Plateau.
