igneous
Basalt River Pebble
Basalt (Mafic Volcanic Rock)
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull/Matte. Crystal structure: Aphanitic (fine-grained). Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark gray to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull/Matte. 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 or near the Earth's surface. This specific specimen has been rounded by mechanical erosion in a river or stream environment.
Uses & applications
Crushed basalt is used in construction (base for roads/railroads). River stones are used in landscaping, massage therapy (hot stones), and as decorative aquarium gravel.
Geological facts
Basalt is the most common rock type on the Earth's surface 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 (relative to size), dark color, and fine-grained texture. Commonly found in volcanic regions, riverbeds, and coastal beaches.
