igneous
Basalt (River Cobble)
Mafic Igneous Rock (Basalt)
Hardness: 6.0; Color: Dark grey to greenish-black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to greenish-black
- Luster
- Dull or earthy
Identified More igneous →
Explore Basalt (River Cobble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.0; Color: Dark grey to greenish-black; Luster: Dull or earthy; Crystal 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 specific specimen has been rounded and smoothed by water transport in a river or stream environment.
Uses & applications
Primarily used in construction (crushed stone, road base, concrete aggregate), landscaping, and as a durable material for hot stone massage.
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 (relative to size), and fine-grained texture. Commonly found in volcanic regions, riverbeds, and coastal areas downstream from volcanic sources.
