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• Section 3.4

• METAMORPHIC ROCKS

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• A. What Metamorphic Rocks Are

• 1. Metamorphic (meta= change, morph= form) rocks are formed from existing rock by the action of heat, pressure, and chemicals.

• 2. There are two types of metamorphism:

• a. Regional metamorphism

• b. Contact metamorphism

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• A. Regional Metamorphism- Regional metamorphism occurs when large areas of rock are under intense heatand pressure, it causes rocks to change form

• 1. pressure squeezes their grains closer together.

• 2. heat and chemicals may rearrange the particles.

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• 1. pressure squeezes their grains closer together.

• 2. heat and chemicals may rearrange the particles.

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• 3. examples are quartzite and marble

• a. quartzite is formed from sandstone

Sandstone Quartzite

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Limestone marble

• b. marble is formed from limestone

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• A. The Metamorphism of Shale

• 1. during regional metamorphism, shale becomes more dense and more crystalline. The elements recombine to form new minerals. The pressures squeezes the materials into parallel layers. The new rock splits easily along these layers. This is called foliation.

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foliation

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• Shale forms slate. In slate, foliation layers are microscopically thin.

Shale

(sedimentary rock)

slate

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• If metamorphism continues, phyllite is formed.

phylliteslate

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• If the process continues, schist is formed (the foliation layers are easily seen).

• 2. schist can be formed from many different rocks;shales, impure sandstones, and basalt.

• 3. schist comes in many varieties, mica schist for example.

schistphyllite

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• 4. gneiss is also a metamorphic rock. It too comes from a variety of rocks. It can be formed from shale, granite, conglomerate and others.

• 5. gneiss has coarse foliation, cardboard-thick parallel foliation.

schist gneiss

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shale

slate

phyllite

schist

gneiss

METAMORPHISM OF SHALE

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Granite Gneiss

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Basalt Gneiss

16Peat

Lignite

Bituminous

Coal

Anthracite Coal

METAMORPHISM OF COAL

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• A. Contact Metamorphism- thermal= heat- thermal metamorphism occurs when hot magma forces its way into overlying rock. The heat bakes the rocks that are in contact with it. Hot liquids and gases may enter the intruded rock and react with its mineral. Only small areas are affected and the changes in the rock are usually less drastic. Foliation is not produced.

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• 1. Hornfels is an example formed from shale that has undergone contact metamorphism. It is very fine-grained, dense, and very hard.

Shale Hornfels

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• A. The Rock Cycle

• 1. igneous rocks are the primary or parent rocks of the crust.

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• 2. igneous rocks are

• weathered and eroded.

• 3. sediments formfrom the igneous rocks.

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• 4. sediments are transported, deposited and eventually buried

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• 5. sediments undergo lithification transforming them into sedimentary rock.

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• 6. igneous and sedimentary rocks may be transformed by heat and pressure into metamorphic rocks.

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• 7. all rock types may be forced deep into the earth by crustal movements where they may remelt and become magma.

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• 8. magma may again cool and become igneous rock.

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• 9. this represents a cycle known as the rock cycle.This cycle has many shortcuts and detours.

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