igneous
Basalt River Pebble
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, weathering to light brown or grey; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black, weathering to light brown or grey
- Luster
- Dull/Matte
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, weathering to light brown or grey; 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 smoothed and rounded by fluvial erosion in a river or stream environment over thousands of years.
Uses & applications
Commonly used in construction aggregate, road base, and concrete. In polished pebble form, it is used for landscaping, aquarium decoration, and massage stones ("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 extensively on the Moon and Mars.
Field identification & locations
Identified in the field by its dark color, heavy weight for its size, and absence of visible large crystals. Most common in volcanic regions and riverbeds downstream from volcanic plateaus.
