igneous
Basalt River Pebble
Basalt (fine-grained mafic igneous rock)
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal; Luster: Dull/matte; Crystal Structure: Microcrystalline (aphanitic); Cleavage: None/conchoidal; Specific Gravity: 2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to charcoal
- Luster
- Dull/matte
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal; Luster: Dull/matte; Crystal Structure: Microcrystalline (aphanitic); Cleavage: None/conchoidal; 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 water-worn and smoothed over thousands of years in a high-energy river or coastal environment.
Uses & applications
Used primarily as construction aggregate, road base, and in decorative landscaping. Polished stones are used in hot stone massage therapy and minor aquarium decor.
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 (lunar maria) and Mars.
Field identification & locations
Identify by its heavy weight (high density), dark color, and lack of visible crystals. It is commonly found in volcanic regions, riverbeds, and gravel pits.
