igneous
Basalt
Extrusive mafic volcanic rock
Hardness: 6-7 (Mohs); Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull to sub-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: 6-7 (Mohs); Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Used extensively in construction for aggregate, road base, asphalt, and concrete. Also used for river rocks in landscaping and hot stone massage therapy.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floors. It is also found on the Moon and Mars.
Field identification & locations
Identify by its heavy weight, dark color, and lack of visible crystals. Commonly found on beaches as smooth pebbles or near volcanic basalt columns.
