igneous
Basalt (River Stone)
Extrusive Mafic Igneous Rock (Basalt)
Hardness: 6.0 (Mohs scale); Color: Charcoal gray to black; Luster: Dull/Matte (aphanitic texture); Crystal structure: Fine-grained; Specific gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Charcoal gray to black
- Luster
- Dull/Matte (aphanitic texture)
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Physical properties
Hardness: 6.0 (Mohs scale); Color: Charcoal gray to black; Luster: Dull/Matte (aphanitic texture); Crystal structure: 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 very near the Earth's surface. This specimen appears water-worn, smoothed over centuries by river or stream action.
Uses & applications
Used primarily in construction for road base, concrete aggregate, and railroad ballast. Smooth river specimens are popular in landscaping, aquarium decor, and massage therapy.
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 in the field by its high density, dark uniform color, and lack of visible individual crystals. Commonly found in volcanic regions or in riverbeds downstream from volcanic plateaus.
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