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Metamorphism usually happens where plates are coming together; rocks are heated and are under high pressure.
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Metamorphic Rocks

Have you have heard that caterpillars metamorphose into butterflies? Rocks can metamorphose too! They change when they are in a place that is very hot with high pressure. One place like this is where the pieces of Earth's outer layer are crashing into each other.

Any type of rock can change into a metamorphic rock. The rocks are changed either in small areas or large areas.

Some rocks only change a little, while others change a lot. When a rock is metamorphosed, its mineral crystals change. Usually, the same chemical ingredients are used to form new crystals during metamorphism. Sometimes new types of minerals grow that weren't in the rock before. Often, flat minerals like mica become lined up forming little layers called foliation.

Figure out foliation!
Try this experiment to figure out how minerals line up when a rock is under pressure.

  1. Add mica flakes to a piece of play dough. The dough will represent a rock undergoing metamorphism.
  2. Knead the dough until the mica flakes are well-incorporated roll your dough into a ball.
  3. Break the ball of dough in half. The flakes will be oriented in all different directions just as they would be in an unmetamorphised rock.
  4. Take one half of the ball and flatten it with the palm of your hand. The pressure that you are applying to the dough is like the pressure placed on our rocky Earth by the forces of plate tectonics.
  5. Break the flattened dough in half and look at what has happened to the mica flakes!


Last modified June 20, 2003 by Lisa Gardiner.

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TES XXVI, 3 fall 2010 The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

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