igneous
Basalt (River Stone)
Basalt
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull/Matte
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull/Matte; Crystal structure: Aphanitic (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 specific specimen has been rounded by fluvial (river) erosion over time.
Uses & applications
Commonly used as river rock for landscaping, in construction as crushed stone or aggregate, and sometimes in hot stone massage therapies.
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 by its dark color, heavy weight for its size, and lack of visible crystals. It is ubiquitous in volcanic regions and riverbeds downstream from volcanic ranges.
