This Planet Really Rocks!
Heat and pressure can change many things. They can even change rocks. The name for rocks that has been changed is metamorphic (met uh MOR fik) rocks. Metamorphic comes from Greek words meaning "change" and "form".
Metamorphic rocks form deep in the earth where high temperature, great pressure, and chemical reactions cause one type of rock to change into another type of rock. Metamorphic rocks begin to form at 12-16 kilometers beneath the earth's surface. They begin changing at temperatures of 100 degrees Celsius to 800 degrees Celsius. If you squeeze and heat a rock for a few million years, it can turn into a new kind of rock.
Where does the heat come from? The heat comes from magma. Where does the pressure come from? The pressure comes from layers of rock piled on top of layers and layers of rock. The layers on the bottom get squeezed. The thicker the layers, the more pressure there is.
Some examples of how metamorphic rocks were changed:
Below is a summary of the major characteristics of metamorphic rocks.
Rarely has fossils
May react with acid
May have alternate bands of light and dark minerals
May be composed of only one mineral, ex. marble & quartzite
May have layers of visible crystals
Usually made of mineral crystals of different sizes
Rarely has pores or openings
May have bent or curved foliation
To learn more about rocks and minerals, click next below:
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