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Metamorphic Rocks

READ HERE about Metamorphic Rocks.  When you are done looking at this page, think about the  different kinds of metamorphic rocks.  Do you have any metamorphic rocks in your house?  See if you are right-go to http://library.thinkquest.org/J002289/uses.html
 
and scroll to the category that says common uses of rocks and minerals.
 

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.

    Classified by texture and composition
    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

 

Fascinating Fact

The oldest known rock lies in Canada. The Acasta gneiss, a metamorphic rock, is 3.96 billion years old