igneous
Basalt (River Pebble)
Basalt
Hardness: 5-6 Mohs. Color: dark gray to black. Luster: dull to mat. Crystal structure: aphanitic (fine-grained). Specific gravity: 2.8-3.0. This specimen shows a smooth, rounded water-worn texture.
- Hardness
- 5-6 Mohs
- Color
- dark gray to black
- Luster
- dull to mat
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: 5-6 Mohs. Color: dark gray to black. Luster: dull to mat. Crystal structure: aphanitic (fine-grained). Specific gravity: 2.8-3.0. This specimen shows a smooth, rounded water-worn texture.
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 and polished through fluvial processes in a river or coastal environment.
Uses & applications
Used extensively in construction (crushed stone, concrete aggregate), high-end floor tiles, and as decorative landscaping stones. Highly polished basalt is popular in massage therapy (hot stones).
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 common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible large crystals. Commonly found in volcanic regions or as smooth pebbles in riverbeds and on beaches.
