igneous
Basalt River Stone
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic, Crystal structure: Fine-grained/Aphanitic, Cleavage: None/Conchoidal fracture, Specific Gravity: 2.8–3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic, Crystal structure: Fine-grained/Aphanitic, Cleavage: None/Conchoidal fracture, Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the surface of a terrestrial planet or moon. This specific specimen has been polished smooth by water action in a river or coastal environment.
Uses & applications
Used extensively in construction as aggregate, road base, and concrete. Smooth specimens like this are used in landscape design, aquarium decor, and hot stone massage therapy.
Geological facts
Basalt is the most common rock on Earth's surface and also makes up most of the ocean floors and the lunar maria on the Moon.
Field identification & locations
Identify by its heavy weight (high density), dark color, and lack of visible large crystals. To distinguish from obsidian, check that it is opaque even on thin edges. Commonly found in volcanic regions and riverbeds.
