Basalt

Mafic extrusive igneous rock

Dark volcanic rock formed when lava cools quickly at the surface.

United States

Sample content • provenance shown broadly for demonstration

At a glance

Fast Facts

igneous

pyroxene + plagioclase + olivine

Rapid cooling of iron-rich lava at the surface

United States

Read the evidence

The Story

Basalt pours from volcanoes and cracks in Earth's crust. Rapid cooling keeps its mineral crystals tiny. Most of the ocean floor is basalt, so this ordinary-looking rock covers more of Earth than any other rock type.

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Where Does It Fit?

Starting material→Rapid cooling of iron-rich lava at the surface→Basalt