igneous
Basalt River Cobble
Basalt (Mafic Igneous Rock)
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.87-3.00
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.87-3.00
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 and smoothed by water transport in a river or coastal environment.
Uses & applications
Used in construction for road base, concrete aggregate, and railroad ballast. Smooth river stones are popular in landscaping and decorative masonry.
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 heavy weight (density), dark color, and fine grain where individual crystals are not visible to the naked eye. Found worldwide in volcanic provinces and riverbeds.
