Metamorphism usually happens where plates are coming together; rocks are heated and are under high pressure.
Have you have heard that caterpillars metamorphose into butterflies? Well, rocks can metamorphose too! They don't grow wings like a butterfly. But they do change! Rocks metamorphose when they are in a place that is very hot and pressure is high. You can find such a place where Earth's tectonic plates are coming together. There, the colliding plates squish rocks, and hot pools of magma heat them deep underground.
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 perpendicular (at a right angle) to the direction of pressure. When minerals within a metamorphic rock are organized this way, it is called foliation. Some metamorphic rocks are foliated and others are non-foliated.
Any type of rock, can be metamorphosed. The rocks are changed either in small areas of contact metamorphism or large areas of regional metamorphism.
Figure out foliation!
Try this experiment to figure out how minerals become oriented when a rock is under pressure.
- Add mica flakes to a piece of play dough. The dough will represent a rock undergoing metamorphism.
- Knead the dough until the mica flakes are well-incorporated roll your dough into a ball.
- 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.
- 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.
- Break the flattened dough in half and look at what has happened to the mica flakes!
Shop Windows to the Universe Science Store!
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!
You might also be interested in:
Basalt is an extrusive igneous rock that is very dark in color. It is the most common type of rock in the Earth's crust and it makes up most of the ocean floor. It is made of many dark colored minerals...more
Many kilometers below the Earth’s surface, molten rock called magma flows into cracks or underground chambers. There, the magma sits, cooling very slowly over thousands to millions of years. As it cools,...more
If you could travel to the center of the Earth, you would find that it gets hotter and hotter as you travel deeper. The heat is naturally produced when radioactive elements break apart. Within the Earth’s...more
Look at granite closely and you can see crystals of common silicate minerals such as quartz, plagioclase feldspar and orthoclase feldspar. In fact, granite is mostly quartz and feldspar crystals. It also...more
As magma cools, elements within it bond together to form crystals of minerals. However, not all minerals can form at the same time during cooling. Some minerals grow when magma is still pretty hot, while...more
Spotting minerals is fun! There are many different types of minerals, each with a different name and a special set of characteristics. So, if you find a mineral that you do not recognize, you can use...more
Quartz is one of the most common mineral in Earth’s crust! Silica (Si) and Oxygen (O) are the only elements within pure quartz. If a cooling magma has silica leftover after feldspars form, quartz is likely...more