METAMORPHIC ROCKS
Rocks that form from other pre-existing
rock (sedimentary, igneous, or metamorphic) that have
been changed from high temperature
and/or high pressure
Metamorphic Rocks
Metamorphic Rocks Formation
Conditions that cause rock to undergo
metamorphism include:
• Heat - Under conditions of high temperature
from magma contacting pre-existing rock.
• Pressure - Deep burial and pressure from
mountain formation.
Types of Metamorphism
1. Contact Metamorphism
2. Regional Metamorphism
Contact Metamorphism
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

Deep burial and pressure from mountain
formation.
The main metamorphic agent is heat.
Also forms when pre-existing rock comes
into contact with molten lava or magma.
The heat from the molten material is hot
enough to cause the minerals in the original
rock to re-crystallize, but not melt.
Regional Metamorphism



Covers large areas typically associated with
mountains
Deep burial and pressure from mountain
formation.
Heat and Pressure change the rock
Types of Metamorphic Rocks

Foliated: rocks with mineral crystals arranged
in cable-like distorted layers/structures
Mineral Alignment
 Banding
 Animation: Foliation


Nonfoliated: rocks with recrystallized
minerals; no layering

Recrystallization: This is the growth of new
mineral crystals from other rocks.
Scheme for Metamorphic Rock Identification
Texture
Composition
MINERAL
ALIGNMENT
BANDING
FOLIATED
Mica
Mica, Quartz,
Feldspar,
Amphiboles, Garnet
Mica, Quartz,
Feldspar,
Amphiboles, Garnet,
Pyroxene
Mica, Quartz,
Feldspar,
Amphiboles, Garnet,
Pyroxene
Type of
Metamorphism
Comment
Rock Name
Regional
Low-Grade
metamorphism of
SHALE
Slate
(Heat and
Pressure
increase w/
depth)
Foliation surfaces shiny
from microscopic mica
crystals
Platy mica crystals
visible
Compact, may split
easily
Phyllite
Schist
Gneiss
Progression of Metamorphism
Start with a shale and then hit
it with heat and pressure!
More
Heat
&
Pressure
Rock Name
Rock Type
Grade of
Metamorphism
Shale
Sedimentary
-----
Slate
Metamorphic
Low
Phyllite
Metamorphic
Low/Intermediate
Schist
Metamorphic
Intermediate/High
Gneiss
Metamorphic
High
Molten Rock
Cools into
Igneous Rock
-----
Shale
(Sedimentary Rock)
Heat
&
Pressure
Slate
(Metamorphic Rock)
Slate
(Metamorphic Rock)
Heat
&
Pressure
Phyllite
(Metamorphic Rock)
Phyllite
(Metamorphic Rock)
Heat
&
Pressure
Schist
(Metamorphic Rock)
With even more heat & pressure
(High-Grade Metamorphism)
… you end up with something
that is really Gneiss!
Scheme for Metamorphic Rock Identification
Texture
Composition
NONFOLIATED
Variable
Type of
Metamorphism
Contact
(Heat)
Quartz
Regional
Calcite and/or
Dolomite
(Heat
&
Pressure)
Various minerals in
particles and matrix
Comment
Various rocks changed
by nearby magma/lava
Metamorphism of
Quartz Sandstone
Metamorphism of
Limestone or
Dolostone
Rock Name
Hornfels
Quartzite
Marble
Pebbles may be
distorted or stretched Metaconglomerate
Citations


Slide 6 (Progression of Metamorphism of Shale)
http://physics.uwstout.edu/geo/_derived/sect4.htm_txt_sect4.2.gif
Slide 10

Shale:
http://library.thinkquest.org/06aug/02459/rocks/sedimentary/Shale.jpg

Slate:
http://www.global-b2b-network.com/direct/dbimage/10260661/Grey_Slate.jpg
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Slide 11:

Phyllite:
http://www.bedford.k12.ny.us/flhs/science/geoscience/images/phyllite.jpg
Slide 12:

Schist (1)
http://www.randall.k12.wi.us/rocks/images/schist-with-garnet.jpg
Schist (2)
http://www.es.ucl.ac.uk/schools/Glossary/schist.jpg


Slide 13:
Gneiss (1)
http://hyperphysics.phy-astr.gsu.edu/hbase/geophys/geopic/gneiss2.jpg

Gneiss (2)
http://www.cropsoil.uga.edu/soilsandhydrology/images/Gneiss.jpg

Gneiss (3)
http://upload.wikimedia.org/wikipedia/commons/6/60/Gneiss.jpg
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Slide 16:

8/16/2006 Physical Setting Regents Earth Science Exam p. 18
Slide 17:

Earth Science Reference Tables p. 6