igneous
Basalt
Basalt (Vitreous to Fine-grained Extrusive Igneous Rock)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic, 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 to sub-metallic, Crystal Structure: Aphanitic (fine-grained), Cleavage: None (conchoidal fracture), Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron at or very near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Used extensively in construction for road base, concrete aggregate, railroad ballast, and as a dimension stone for flooring or monuments.
Geological facts
Basalt is the most common rock in Earth's crust and covers 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 lack of visible crystals to the naked eye. Often found in volcanic fields or as river-tumbled cobbles.
