Basalt
“The floor of the ocean”
Igneous
Basalt is a dark, fine-grained extrusive igneous rock and the most common rock type on Earth's surface. It forms from the rapid cooling of lava rich in magnesium and iron, and makes up nearly all of the oceanic crust.
Composition
plagioclase feldspar, pyroxene, olivine
Where Found
Hawaii (USA), Iceland, Giant's Causeway (Northern Ireland), Deccan Traps (India)
Mohs Hardness
6
Fun Fact
The Giant's Causeway in Northern Ireland features about 40,000 interlocking basalt columns formed by an ancient volcanic eruption.
Test Your Knowledge
Why does basalt commonly form hexagonal columnar joints when it cools?
Related Specimens
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