igneous
Basalt (River Stone)
Basalt (composed mostly of plagioclase, pyroxene, and olivine)
Hardness: 6-7 (Mohs scale), Color: Dark grey to charcoal, Luster: Dull/Matte (aphanitic), Crystal structure: Fine-grained/Microcrystalline, Specific gravity: 2.8-3.0
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey to charcoal, Luster: Dull/Matte (aphanitic), Crystal structure: Fine-grained/Microcrystalline, 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. Extrusive volcanic origin. The smooth texture indicates it has been water-worn in a river or coastal environment.
Uses & applications
Extensively used in construction as aggregate, road base, and railroad ballast. Also used for hot stone massage therapy and decorative aquarium landscaping.
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
Identified by its dark color, heavy weight compared to its size, and absence of visible large crystals. Commonly found in volcanic regions and transported via river basins.
