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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
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
Foliated –vs- Non-foliated Metamorphic Textures
Foliated – looking at thin section under microscope
Non-foliated – looking at thin section under microscope
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
Foliated Texture
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).
Changes undergone to rocks during metamorphism
Slaty Cleavage Foliation
Slate
Phyllite
Phyllite
Schistosity Foliation
Schist
Mica Schist
Garnet Schist
Banding in Foliation
Gneiss
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
Types of Metamorphism
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 ( )
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)
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)
Examples of Metamorphic Rocks
Quartzite – parent rock is Sandstone
Examples of Metamorphic Rocks
Marble – parent rock is Limestone
Examples of Metamorphic Rocks
Slate – parent rock is Shale
Examples of Metamorphic Rocks
Phyllite – parent rock is Shale
Examples of Metamorphic Rocks
Schist – parent rock is Shale (sometimes granite or other rocks, depending on the content)
Mica Schist
Garnet Schist
Examples of Metamorphic Rocks
Gneiss – parent rock is Shale, Granite, or conglomerate (sometimes other rocks, depending on the content)
(Metamorphic Website)
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