igneous
Basalt (River Stone)
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6-7 (Mohs scale), Color: Dark grey to charcoal, Luster: Dull/Matte, Crystal structure: Aphanitic (fine-grained/microscopic), 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, Crystal structure: Aphanitic (fine-grained/microscopic), Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the surface. This specific specimen has been rounded and smoothed by water erosion in a fluvial (river) or glacial environment.
Uses & applications
Used in construction as crushed stone, road base, concrete aggregate, and for railroad ballast. High-quality smooth stones are used in massage therapy (hot stone massage) and 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, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and very fine-grained texture. It will not scratch easily with a steel nail. Common in volcanic regions and riverbeds.
