igneous
Basalt (River Stone)
Basalt
Hardness: 5-6 Mohs. Color: Dark gray to black, often weathering to brown. Luster: Dull to earthy. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. Specific gravity: 2.8–3.0. Cleavage: None.
- Hardness
- 5-6 Mohs
- Color
- Dark gray to black, often weathering to brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray to black, often weathering to brown. Luster: Dull to earthy. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. Specific gravity: 2.8–3.0. Cleavage: None.
Formation & geological history
Extrusive volcanic rock formed from the rapid cooling of magnesium-rich and iron-rich lava. This specimen has been rounded and smoothed by fluvial erosion in a river or coastal environment.
Uses & applications
Used primarily in construction (crushed stone, asphalt aggregate), for river rock landscaping, and in hot stone massage therapy. Some varieties are used by lapidaries for carving.
Geological facts
Basalt is the most common rock in Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (high density), and fine-grained texture. Commonly found in volcanic regions or in riverbeds downstream from volcanic sources. Collectors look for unique shapes created by water erosion.
