Metamorphism also known as thermal metamorphism

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Metamorphic Rocks
Rocks that are formed by heat and/or
pressure
(but not completely melted)

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Metamorphic rocks are formed by:
• Regional metamorphism
–Involves mostly pressure
• Contact metamorphism
–Involves mostly heat

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Metamorphism by Pressure
What do you think causes enough
pressure to metamorphose miles of
rock?

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Causes flattening of mineral
crystals

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Metamorphism by Pressure
• Pressure often causes realignment
of intergrown mineral crystals
–Called banding
–Or foliation
banding
foliation

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Banding

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Foliation

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Regional Metamorphism
• Mountain building activity
• Involves large areas

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Large-scale
metamorphism

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Metamorphism by Heat
Known as contact metamorphism

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Contact Metamorphism
• Also known as thermal
metamorphism
–Creates baked rock
• ex. hornfels

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Contact Metamorphism
• Igneous intrusion
–Where molten rock is forced
between existing rock
–Tends to bake (metamorphose)
part of the existing rock

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Increasing degrees of metamorphism
Rocks
melt
in
this
range

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Composition of metamorphic rock is
determined by:
• Conditions of metamorphism
• Mineralogy of parent (original)
rock

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limestone marble
Great heat and pressure
(small crystals) (large crystals)
In this example the mineral composition
stays the same

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shale slate
In this example the minerals in shale
actually change into other
minerals during metamorphosis

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• Some metamorphic rocks
can form from several
different parent rocks
–Ex. Gneiss may form from
sandstone, shale or granite

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 Where can you find this image?

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 When sandstone is subjected to heat and or
pressure it becomes what?
 Is marble a foliated or non-foliated
metamorphic rock?
 Name three minerals in schist
 What is the only metamorphic rock in your
ESRT that exhibits banding?

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How to identify rocks
Interlocking crystals?
Igneous/metamorphic sedimentary
banding/foliation?
metamorphic igneous

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Rocks
• All rocks are classified on the basis
of how they formed
–Sedimentary rocks form from bits and
pieces of existing rock
–Igneous rocks form from molten
minerals
–Metamorphic rocks form from existing
rocks that are changed by heat and/or
pressure

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Rock Cycle

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Rock Cycle
• Nearly all rocks are formed from other
rocks
• Exceptions include
–coal
–Fossil limestone
• Some rocks exist for thousands to
billions of years before undergoing
change

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