igneous
Basalt River Pebble
Extrusive Mafic Basalt
Hardness: 6 (Mohs scale), Color: Dark grey to greenish-black, Luster: Dull to sub-metallic on fresh surfaces, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8 - 3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to greenish-black, Luster: Dull to sub-metallic on fresh surfaces, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, 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 surface. This specific specimen has been water-worn and smoothed in a river or coastal environment.
Uses & applications
Common basalt is used in construction as aggregate, road base, and railroad ballast. Smooth river stones are popular in landscaping and home decor.
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 (high density), dark color, and fine-grained texture. Commonly found in volcanic regions or in riverbeds downstream from volcanic highlands.
