igneous
Basalt River Cobble
Basalt
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to waxy when wet; Structure: Aphanitic (fine-grained); Cleavage: None; SG: 2.8-3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to waxy when wet
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to waxy when wet; Structure: Aphanitic (fine-grained); Cleavage: None; SG: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava. This specific specimen has been rounded by mechanical erosion in a high-energy aquatic environment such as a river or beach.
Uses & applications
Used in construction as road base, concrete aggregate, and railroad ballast. Smooth river stones are popular in decorative landscaping and masonry.
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 and Mars.
Field identification & locations
Identified by its heavy weight (high density), dark color, and fine-grained texture. Commonly found in volcanic regions or transported far by glacial and fluvial action.
