igneous
Basalt (Weathered)
Basalt
Hardness: 5-6 (Mohs), Color: Dark grey to brownish-grey when weathered, Luster: Dull or earthy, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8-3.0.
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Physical properties
Hardness: 5-6 (Mohs), Color: Dark grey to brownish-grey when weathered, Luster: Dull or earthy, Crystal 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 or near the Earth's surface. Basalt is the most common rock type in the Earth's crust (especially the ocean floor).
Uses & applications
Commonly used as crushed stone for construction projects, road base, concrete aggregate, and railroad ballast.
Geological facts
Basalt covers about 70 percent of Earth's surface. It is also common on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight for its size, and very fine-grained texture. It often weathers to a rusty or light brown color due to iron oxidation. Found worldwide in volcanic regions.
