Download Metamorphic Rock

Name:
Objective: I can explain how metamorphic rocks are
formed.
Date:
Homeroom:
Handout #: 2.6
Objective: I can explain how metamorphic rocks are formed.
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1. How are sedimentary rocks and igneous rocks different in how they form?
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2. How are sedimentary and igneous rocks different in where they form?
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Objective: I can explain how metamorphic rocks are formed.
Metamorphic Rock
Have you ever watched a caterpillar change into a butterfly? Some caterpillars go through
a biological process called metamorphosis in which they completely change their shape.
Rocks can also go through a process called metamorphism. The word metamorphism comes
from the Greek words meta, which means “changed,” and morphos, which means “shape.”
Metamorphic rocks are rocks in which the structure, texture, or composition of the rock have
changed. All three types of rock can be changed by heat, pressure, or a combination of
both.
Origins of Metamorphic Rock
Metamorphic rocks arise from the transformation of existing rock types. The original rock is
subjected to extreme heat and pressure causing profound physical and/or chemical
change. The original rock may a sedimentary rock, and igneous rock, or another older
metamorphic rock.
The temperature at which most metamorphism occurs ranges from 50°C to 1,000°C.
However, the metamorphism of some rocks takes place at temperatures above 1,000°C. It
seems that at these temperatures the rock would melt, but this is not true of metamorphic
rock. It is the depth and pressure at which metamorphic rocks form that allows the rock to
heat to this temperature and maintain its solid nature. Most metamorphic change takes
place at depths greater than 2 km. But at depths greater than 16 km, the pressure can be
4,000 times greater than the pressure of the atmosphere at Earth’s surface.
Metamorphic rocks may be formed simply by being deep beneath the Earth’s surface,
subjected to high temperatures and the great pressure of the rock layers above it. They can
form from tectonic processes such as continental collisions, which cause horizontal pressure
and friction. They are also formed around magma chambers in Earth’s interior.
1. How is metamorphic rock formed?
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2. Does rock melt before it transforms into metamorphic rock?
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3. Metamorphic rocks form when extreme ________________________________ and
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Contact Metamorphism
One way rock can undergo metamorphism is by being heated by nearby magma. When
magma moves through the crust, the magma heats the surrounding rock and changes it.
Some minerals in the surrounding rock are changed into other minerals by this increase in
temperature. The greatest change takes place where magma comes into direct contact
with the surrounding rock. The effect of heat on rock gradually decreases as the rock’s
distance from the magma increases and as temperature decreases. Contact
metamorphism occurs near igneous intrusions, as shown below.
Regional Metamorphism
When pressure builds up in rock that is buried deep below other rock formations or when
large pieces of the Earth’s crust collide with each other, regional metamorphism occurs. The
increased pressure and temperature causes rock to become deformed and chemically
changed. Unlike contact metamorphism, which happens near bodies of magma, regional
metamorphism occurs over thousands of cubic kilometers deep within Earth’s crust. Rocks
that have undergone regional metamorphism are found beneath most continental rock
formations.
4. What are two differences between contact and regional metamorphism?
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Composition of Metamorphic Rock
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Metamorphism occurs when temperature and pressure inside the Earth’s crust change.
Minerals that were present in the rock when it formed may not be stable in the new
temperature and pressure conditions. The original minerals change into minerals that are
more stable in these new conditions. Look at the figure below to see an example of how this
change happens.
twig video: Rock Types - https://www.twigcarolina.com/film/rock-types-3238/
5. Fossils are found in what type of rock? _________________________________
6. Which type of igneous rock has small crystals? ________________________________
7. How does metamorphic rock form? ____________________________________________________
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QUESTIONS
8. Where does metamorphic rock form?
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9. Why does metamorphic rock form in those areas?
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10. How are igneous rock and metamorphic rock different in how they form? Which one
requires rock to melt? How are they similar?
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11. Which type of rock is most likely to form on Earth’s surface? Why?
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12. Which type of rock forms deepest in the Earth’s crust? Why?
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13. How are metamorphic rock and sedimentary rock different in how they form?
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