igneous
Basalt
Basalt (various silicate compositions)
Hardness: 6 (Mohs scale), Color: Dark gray to black, Luster: Dull/Submetallic, Crystal structure: Aphanitic (fine-grained), Cleavage: None/Conchoidal, Specific gravity: 2.8 - 3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark gray to black, Luster: Dull/Submetallic, Crystal structure: Aphanitic (fine-grained), Cleavage: None/Conchoidal, 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 rock). Found in volcanic regions and oceanic crust.
Uses & applications
Widely used in construction for road base, concrete aggregate, and railroad ballast. Also used as stone for architectural tile and in decorative 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 by its dark color, heavy weight (relative to size), and fine-grained texture with no visible individual crystals. Common in volcanic fields and coastlines.
