igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic, Crystal structure: Aphanitic (fine-grained), 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/Submetallic, Crystal structure: Aphanitic (fine-grained), 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 exposed at or very near the Earth's surface. Found in oceanic crust, volcanic islands, and flood basalt provinces.
Uses & applications
Used primarily in construction for road base, concrete aggregate, railroad ballast, and high-quality stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and it also makes up most of the surface of the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture lacking visible crystals. Common in areas of past volcanic activity.
