igneous
River Stone (Basalt Porphyry)
Basalt (with possible olivine or plagioclase phenocrysts)
Hardness: 6-7 Mohs; Color: Dark grey to olive-greenish black; Luster: Dull/earthy (weathered); Structure: Fine-grained matrix (aphanitic) with coarser visible grains (porphyritic); Specific gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Dark grey to olive-greenish black
- Luster
- Dull/earthy (weathered)
Identified More igneous →
Explore River Stone (Basalt Porphyry) 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 olive-greenish black; Luster: Dull/earthy (weathered); Structure: Fine-grained matrix (aphanitic) with coarser visible grains (porphyritic); Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specimen has been rounded and smoothed by water transport in a river or coastal environment.
Uses & applications
Commonly used as decorative landscaping stone, in construction as crushed aggregate, or as aquarium decor. Certain varieties are used for hot stone massage therapy due to heat retention.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The pitted circular feature on this specimen is likely a 'chatter mark' or a percussion scar from colliding with other rocks in high-energy water.
Field identification & locations
Identify by its dark color, heavy weight for its size, and fine-grained texture. Found globally in volcanic regions and riverbeds. Look for the smooth, water-worn exterior and 'conchoidal' (shell-like) chips if broken.
