igneous
Basalt River Pebble
Basalt (Mafic volcanic rock)
Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull to earthy; Structure: fine-grained (aphanitic); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- dark grey to black
- Luster
- dull to earthy
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull to earthy; Structure: fine-grained (aphanitic); 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 by fluvial (river) or coastal erosion processes.
Uses & applications
Commonly used as high-quality aggregate in road construction, concrete, and railroad ballast. Smooth river stones are popular for landscaping, zen gardens, 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 in large quantities on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible large crystals. Commonly found in volcanic regions, riverbeds, and beaches.
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