JEREMY WALKER / SCIENCE PHOTO LIBRARY JEREMY WALKER / SCIENCE PHOTO LIBRARY
Basalt columns, with a man standing at upper left. These columns of basalt formed when molten rock (magma) from below the Earth's surface rose to the surface during volcanic activity. Rocks of magmatic origin are called igneous rocks. As these igneous rocks formed at the surface, they are called extrusive igneous rocks. The geometry of the columns is due to contraction on cooling. Photographed in Iceland.
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