igneous
Basalt
Extrusive Igneous Rock
AI-generated identification · may be incorrectHardness 6 on Mohs scale, dark gray to black color, dull to sub-aphanitic luster, fine-grained aphanitic crystal structure, specific gravity around 2.8 to 3.0.
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Physical properties
Hardness 6 on Mohs scale, dark gray to black color, dull to sub-aphanitic luster, fine-grained aphanitic crystal structure, specific gravity around 2.8 to 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the Earth's surface, dating from Precambrian to recent geological eras.
Uses & applications
Used widely in construction as crushed stone for aggregate, road base, asphalt, and railroad ballast, as well as in manufacturing stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crustal portions underlying the ocean basins and forms massive volcanic formations like the Giant's Causeway.
Field identification & locations
Identify in the field by its dark color, heavy feel, and fine-grained texture; found abundantly worldwide in volcanic provinces and oceanic islands.
