igneous
Basalt
Mafic extrusive igneous rock
Hardness of 6 on the Mohs scale; dark gray to black in color; dull to sub-withish luster; fine-grained aphanitic crystal structure; specific gravity around 2.8-3.0.
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Physical properties
Hardness of 6 on the Mohs scale; dark gray to black in color; dull to sub-withish luster; fine-grained aphanitic crystal structure; specific gravity around 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the Earth's surface, often from volcanic eruptions or oceanic crust formation.
Uses & applications
Used in construction as crushed stone for road base, concrete aggregate, railroad ballast, and in the production of stone wool insulation.
Geological facts
Basalt is the most common rock type on Earth's crust, making up most of the ocean floor and also found extensively on the Moon and Mars.
Field identification & locations
Easily identified in the field by its dark color, fine-grained texture, and high density. Found globally in volcanic regions, island arcs, and continental flood basalt provinces.
