igneous
Basalt
Extrusive igneous rock
AI-generated identification · may be incorrectHardness 6 on Mohs scale; dark grey to black color; dull to sub-to-earthy luster; fine-grained aphanitic crystal structure; specific gravity 2.8-3.0.
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Physical properties
Hardness 6 on Mohs scale; dark grey to black color; dull to sub-to-earthy luster; fine-grained aphanitic crystal structure; specific gravity 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.
Uses & applications
Widely used in construction, road aggregate, railroad ballast, and production of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor and major volcanic islands like Hawaii.
Field identification & locations
Identify by its dark, fine-grained matrix and vesicular texture; common globally in volcanic provinces and oceanic ridges.
