igneous
Basalt (River Stone)
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs); Color: Dark grey to black (lighter when dry); Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) to porphyritic; Specific Gravity: 2.8-3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black (lighter when dry)
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black (lighter when dry); Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) to porphyritic; 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 smoothed and rounded by river erosion over hundreds to thousands of years.
Uses & applications
Used widely in construction as crushed stone, concrete aggregate, and railroad ballast. Smooth river versions are popular in landscaping, aquariums, and massage therapy (hot stones).
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. Commonly found in volcanic regions, riverbeds, and along shorelines.
