igneous
Basalt (River Pebble)
Extrusive Mafic Igneous Rock
Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull/Sub-metallic (when wet); Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull/Sub-metallic (when wet)
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: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull/Sub-metallic (when wet); 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 the earth's surface. This specimen has been rounded by fluvial (river) or coastal erosion processes.
Uses & applications
Used in construction as aggregate, road base, and high-quality railroad ballast. Polished stones are used in decorative landscaping and stone massage therapy.
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
Identify by its heavy weight (high density), dark matte color, and lack of visible crystals to the naked eye. Commonly found on volcanic beaches and in riverbeds flowing from volcanic highlands.
