igneous
Basalt River Pebble
Extrusive mafic igneous rock
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull/Matte; Structure: Fine-grained aphanitic; Cleavage: None; Specific Gravity: 2.8–3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black
- Luster
- Dull/Matte
Identified More igneous →
Explore Basalt River Pebble 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 grey to black; Luster: Dull/Matte; Structure: Fine-grained aphanitic; Cleavage: None; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. This specimen has been rounded and smoothed by fluvial (river) or glacial erosion over thousands of years.
Uses & applications
Used in construction as road base, railroad ballast, and in concrete. Small rounded pebbles are popular for landscaping, aquarium decor, and zen gardens.
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
Look for a heavy, dark-colored, fine-grained rock with a smooth, rounded surface. Found worldwide in riverbeds, beaches, and volcanic regions.
