MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY
Metamorphic gneiss rocks in the Swiss Alps. The water down centre separates two types of gneiss: orthogneiss (left) and paragneiss (right). Gneiss rocks form by metamorphic processes (heat and pressure at depth) that alter pre-existing igneous or sedimentary rocks. If the gneiss formed from igneous rock, it is known as orthogneiss. If it formed from sedimentary rock it is known as paragneiss. Orthogneiss is a light grey colour, while paragneiss is a darker, redder colour and sedimentary layers are still seen. Photographed on the Verzasca River near the village of Lavertezzo (church in background), Switzerland. The rocks were formed and raised to the surface as the Alps mountain range formed, and have here been eroded and shaped by the river and the weather.
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