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Earth's Surface
3.4
Metamorphic rocks form as existing rocks
change.
Heat and pressure change rocks
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Metamorphism is the process in which an existing rock is
changed by heat and/or pressure
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Parent rock can be sedimentary, igneous, or metamorphic
rock.
The resulting rock is a metamorphic rock.
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Limestone is the parent rock of marble, used by
builders and artists.
Shale can be the parent rock of schist, a source of the
gemstone garnet and a source of the mineral graphite
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During metamorphism, rocks undergo many changes.
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Pressure can cause a rock’s minerals to flatten out in one direction.
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Minerals can change but the rock remains solid.
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Rocks do not melt when they undergo metamorphism
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High temperatures create an igneous rock
Heat and pressure can break the bonds that join atoms in minerals, which
form new bonds
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Two main results
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Crystals can grow larger as more atoms join their crystal structures
New minerals can form in place of older ones as atoms combine in
different ways
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Ex. shale is formed from silt and clay but during
recrystallization, garnet can form from these materials.
Metamorphic changes occur over large and small areas.
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5A.When both temperature and pressure are high
metamorphic changes can occur over very large areas.
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6. In a region where large blocks of rock are pressing
together and pushing up mountain ranges the
process can affect an area hundreds of kilometers
wide and tens of kilometers deep.
Rocks are buried, pressed together, bent, and heated,
and the pressure and heat cause the rocks to
undergo metamorphism.
Metamorphic changes are greater the deeper
beneath the surface
Ex. A sedimentary rock may change to slate near the
surface but become gneiss deep inside a mountain.
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Metamorphic changes occur over large and small
areas.
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5B. Metamorphic changes can occur over small
areas with either high temperature or high pressure.
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Magma can push into rocks underground, or
surface rock can be covered by a lava flow.
7A. Magma or lava heats rock and causes
recrystallization
The thickness of rock changed depends on the
temperature of the molten rock
7B.Rocks moving past each other during an
earthquake can be exposed to pressures high
enough to cause metamorphic changes
Most metamorphic rocks develop bands of minerals.
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8. Foliation is present in most metamorphic rocks
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Minerals are arranged in flat or wavy parallel bands.
Foliated rocks either split easily into leaflike sheets or have bands of
minerals that are lined up and easy to see.
Develops when rocks are under pressure.
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Common in rocks produced by metamorphic changes that affect large
areas.
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9A. Develops when minerals flatten out or line up in bands.
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Bands are extremely thin at low levels of morphism
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With higher pressure and temperature, the mineral mica can grow and
make the rock look shiny, as is common in phyllite and schist.
9B. At high levels of metamorphism, the minerals tend to separate into
light and dark bands, like those in gneiss.
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Metamorphic rocks that do not show foliation are called nonfoliated rocks.
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A metamorphic rock may not display foliation because it is made up of
only one type of mineral.
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Marble, which develops from limestone is used as a decorative
stone because it does not split into layers as an artist is working
with it
Quartzite forms from sandstone that is made up almost entirely of
pieces of quartz.
A metamorphic rock may lack foliation because it has not been
subjected to high pressure.
Hornfels often forms when magma or lava touches other rock