igneous
Basalt (River Pebble)
Extrusive mafic igneous rock
Hardness: 6 (Mohs), Color: Charcoal grey to dark green, Luster: Dull/Matte, Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8-3.0
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Physical properties
Hardness: 6 (Mohs), Color: Charcoal grey to dark green, Luster: Dull/Matte, 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 the Earth's surface. This specimen has been rounded by fluvial erosion in a river or coastal environment.
Uses & applications
Used in construction as crushed stone, road base, or aggregate. Smooth river stones of this type are popular in landscaping and decorative aquariums.
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 dark color, heavy weight compared to other similar-sized stones, and fine-grained texture lacking visible crystals. Commonly found in volcanic regions and riverbeds downstream from volcanic sources.
