igneous
Basalt River Pebble
Extrusive mafic volcanic rock
Hardness: 6 (Mohs scale); Color: Dark gray to black (brownish weathered exterior); Luster: Dull/Earthy; Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black (brownish weathered exterior)
- Luster
- Dull/Earthy
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 (Mohs scale); Color: Dark gray to black (brownish weathered exterior); Luster: Dull/Earthy; Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen has been rounded by fluvial (river) erosion over many years.
Uses & applications
Basalt is used as aggregate in construction, road base, and railroad ballast. Smooth river stones are popular in landscaping and decorative 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 extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and lack of visible crystals. Commonly found in riverbeds, volcanic regions, and coastal areas.
