igneous
Basalt (River Stone)
Basalt (SiO2 range 45-52%)
Hardness: 6.0 on Mohs scale; Color: dark grey to black; Luster: dull/earthy; Crystal structure: aphanitic (fine-grained); Cleavage: none; Specific gravity: 2.8-3.0.
- Hardness
- 6
- Color
- dark grey to black
- Luster
- dull/earthy
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Physical properties
Hardness: 6.0 on Mohs scale; Color: dark grey to black; Luster: dull/earthy; Crystal structure: aphanitic (fine-grained); Cleavage: none; 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 surface. This particular specimen is a water-worn river cobble, likely of Cenozoic or Mesozoic age depending on the location of the river bed.
Uses & applications
Commonly used as crushed stone for road base, concrete aggregate, and railroad ballast. Smooth river-worn versions are popular for decorative landscaping and 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 on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It will not react with acid like limestone.
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