igneous
Basalt River Pebble
Basalt
Hardness: 6 (Mohs). Color: Dark gray to black, weathered to brownish-green. Luster: Dull to earthy. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. Specific gravity: 2.8-3.0.
- Hardness
- 6 (Mohs)
- Color
- Dark gray to black, weathered to brownish-green
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 (Mohs). Color: Dark gray to black, weathered to brownish-green. Luster: Dull to earthy. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. This specific piece has been smoothed by fluvial action (river tumbling).
Uses & applications
Commonly used as crushed stone for construction projects, road base, and railroad ballast. Smooth river-worn specimens are popular in decorative landscaping and as 'worry stones'.
Geological facts
Basalt is the most common volcanic rock on Earth and actually makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identified in the field by its dark color, heavy weight, and fine-grained texture. To distinguish from chert, note the lack of conchoidal fracturing and its generally higher density. Commonly found in volcanic regions or riverbeds downstream from volcanic sources.
