igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 on Mohs scale; Color: Dark grey to black, often with a weathered brown exterior; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8–3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black, often with a weathered brown exterior
- 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, often with a weathered brown exterior; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic lava) at or very near the Earth's surface. It can be found in oceanic crust, volcanic islands, and continental flood basalts.
Uses & applications
Extensively used in construction for aggregate, road base, concrete, and railroad ballast. High-density varieties are used in sea walls. Fine specimens may be used for stonework or as decorative landscape rocks.
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.
Field identification & locations
Identify by its heavy weight (density), dark color, and very fine-grained texture. It often shows a weathered 'rind' that is lighter in color than the fresh interior. Found commonly in volcanic regions such as Hawaii, Iceland, and the Pacific Northwest.
