igneous
Basalt
Extrusive mafic rock (Basalt)
Hardness: 6 (Mohs scale); Color: Dark grey to black with possible weathering to brown; Luster: Dull to somewhat vitreous; Crystal structure: Aphanitic (fine-grained); Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black with possible weathering to brown
- Luster
- Dull to somewhat vitreous
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 with possible weathering to brown; Luster: Dull to somewhat vitreous; Crystal structure: Aphanitic (fine-grained); 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. This specimen appears water-worn from a river or beach environment.
Uses & applications
Used primarily in construction for road base, concrete aggregate, and railroad ballast. Compact, weathered basalt can also be used in river-stone landscaping or as a lapidary material for polishing.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It also exists on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture which lacks visible crystals. Commonly found along coastlines, volcanic islands, and oceanic ridges.
