Download Metamorphic rocks form as existing rocks change.

KEY CONCEPT
Metamorphic rocks form
as existing rocks change.
STANDARDS
8–3.7 Illustrate the creation and changing of
landforms that have
occurred through geologic processes (including volcanic eruptions
and mountain-building
forces).
VOCABULARY
metamorphism p. 96
recrystallization p. 97
foliation p. 100
BEFORE, you learned
NOW, you will learn
• Igneous rocks form as molten
rock cools
• Sedimentary rocks form from
earlier rocks
• How a rock can change into
another type of rock
• How new minerals can grow
in existing rocks
THINK ABOUT
How does a rock change into another
kind of rock?
Examine a sample of shale and a sample
of schist (shihst). Shale, a sedimentary
rock, can change into schist. Think
about how this change could occur
without the shale’s melting or breaking
apart. Make a prediction about what
process changes shale into schist.
shale
schist
Heat and pressure change rocks.
When you cook popcorn, you use heat to increase the pressure within
small, hard kernels until they explode into a fluffy snack. Cooking
popcorn is just one example of the many ways in which heat and
pressure can change the form of things—even things like rocks.
Rocks change into other
rocks by the process of
metamorphism. A similar
word, metamorphosis,
refers to what happens
when a caterpillar changes
into a butterfly.
The process in which an existing rock is changed by heat or
pressure—or both—is called metamorphism (MEHT-uh-MAWR-FIHZuhm). The original sedimentary or igneous rock is called the parent
rock. The resulting rock is a metamorphic rock. Even a metamorphic
rock can be a parent rock for another type of metamorphic rock.
Many of the metamorphic rocks people use were once sedimentary rocks. Limestone is the parent rock of marble, which is used by
builders and artists. Shale can be the parent rock of schist, which can
be a source of the gemstone garnet. Some schists are a source of the
mineral graphite, which is used in pencils.
Give an example of a way people use metamorphic rocks.
96 Unit 1: Earth’s Surface