Download Metamorphic rock is the result of the transformation of an existing

Metamorphic Rocks
Metamorphic rock is the result of the transformation of an existing rock type in a
process called metamorphism, which means "change in form". The existing
rock, (called a protolith), is subjected to heat and pressure (temperatures
greater than 150 to 200 °C and pressures of 1500 bars) causing profound
physical and/or chemical change. The protolith may be sedimentary rock,
igneous rock or another older metamorphic rock. Metamorphic rocks make up
a large part of the Earth's crust.
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. They are also formed when rock is heated up by
the intrusion of hot molten rock called magma from the Earth's interior.
Extremely hot water deep underground can also cause chemical and physical
changes in rock, forming metamorphic rocks.
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.
The study of metamorphic rocks (now exposed at the Earth's surface following
erosion and uplift) provides us with very valuable information about the
temperatures and pressures that occur at great depths within the Earth's crust.
Metamorphic rocks can be classified in two ways. Foliated metamorphic rocks
are those which have alternating visible layers or bands. Non-foliated
metamorphic rocks have no layers or bands.
Some examples of foliated metamorphic rocks are gneiss and schist. Examples
of non-foliated metamorphic rocks are slate, marble, and quartzite.
Below is a summary of the major characteristics of metamorphic rocks.
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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
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Some examples of how metamorphic rocks were changed:
Questions:
1) What does the term ‘metamorphism’ mean?
2) What is a ‘protolith’?
3) What are the two main forces that cause rocks to become metamorphic?
4) How does a studying metamorphic rock at the surface help us understand
the interior of the earth?
5) List the two classifications of metamorphic rocks and give an example of
each.