igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic, Crystal structure: Aphanitic (fine-grained) to porphyritic, 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) to porphyritic, 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. Common in oceanic crust and volcanic regions.
Uses & applications
Used extensively in construction as crushed stone for road base, railroad ballast, and concrete aggregate. Also used for making stone wool (insulation material).
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 (density), and fine-grained texture. It may contain small green crystals of olivine. Commonly found near volcanic sites and ocean ridges.
