MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY
Pegmatite intrusion into gneiss rock. Pegmatite (vertical white band) is a type of igneous rock. An igneous rock rises in a molten state from depth and solidifies as it intrudes into pre-existing rock or reaches the surface. Here, the pegmatite has intruded into paragneiss, a metamorphic rock that was formed earlier when sedimentary rock was altered by pressure and heat at depth. These rocks are in the Swiss Alps, and were formed, raised to the surface, and exposed by erosion, as the Alps mountain range formed. Intrusions like this help to determine the relative ages of the rocks. Photographed on the Verzasca River near Lavertezzo in Switzerland.
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