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Metamorphic RocksGneiss
Metamorphic rocks are: the result of the application of heat, pressure and directed stress, or some combination of these effects applied to pre-existing rock of any type.
The process by which metamorphic rocks are produced is called metamorphism. Slate
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Metamorphic Rocks
2 TYPES OF TEXTURES – FOLIATEDAND NON-FOLIATED
Foliated = banded rock, minerals are arranged in bands, or thin sheets/layers
Non-foliated = unbanded rock, usually consist of all one type of mineral so may appear to have a granular or uniform texture
Ex.) quartz (sand grains) makes up quartzite, calcite (limestone) makes up marble
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Foliated –vs- Non-foliated Metamorphic Textures
Foliated – looking at thin section under microscope
Non-foliated – looking at thin section under microscope
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Foliated Texture
Forms when minerals (many of which are platy micas such as biotite and muscovite) line up producing a
distinct layering in the rock.
Minerals tend to line up perpendicular to the pressure
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Foliated Texture
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Foliated Texture
The layering of minerals produces three distinctly different looking rocks, those with slaty cleavage (e.g. slate), schistosity (e.g. schist), and mineral banding (or gneiss texture).
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Changes undergone to rocks during metamorphism
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Slaty Cleavage Foliation
Slate
Phyllite
Phyllite
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Schistosity Foliation
Schist
Mica Schist
Garnet Schist
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Banding in Foliation
Gneiss
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TYPES OF METAMORPHISM:
REGIONAL – large scale metamorphism (over large areas , up to thousands of square feet) – think mountains
LOCAL – smaller scale metamorphism
Contact – think burn on
your finger
Deformational/Dynamic –think bent finger – smashedin the door
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Types of Metamorphism
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Regional Metamorphism
Occurs during mountain building
On a large scale (over large areas)
Forms most of the metamorphic rocks of Earth’s crust
Rocks are subject to high heat and high pressure
The result is a rock that has pronounced foliation and layering.(The foliation is usually perpendicular to the direction of the applied stress.)
T, P ( )
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Local Metamorphism –
Contact
Occurs on a smaller scale
when hot magma (liquid and gases) move into the parent/country rock, heating and changing it. (so
its close to magma)
Usually non-foliated and appear to have a sugary texture
( T)
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Local Metamorphism –Deformational/Dynamic
Occurs on a smaller scale
in fault zones (so friction & pressure change the rock)
Can have sugary texture (non-foliated) or be foliated
( T, P)
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Examples of Metamorphic Rocks
Quartzite – parent rock is Sandstone
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Examples of Metamorphic Rocks
Marble – parent rock is Limestone
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Examples of Metamorphic Rocks
Slate – parent rock is Shale
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Examples of Metamorphic Rocks
Phyllite – parent rock is Shale
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Examples of Metamorphic Rocks
Schist – parent rock is Shale (sometimes granite or other rocks, depending on the content)
Mica Schist
Garnet Schist
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Examples of Metamorphic Rocks
Gneiss – parent rock is Shale, Granite, or conglomerate (sometimes other rocks, depending on the content)
(Metamorphic Website)