Metamorphic Rocks # 2
9/28/2005
Types of Metamorphic Rocks
• Metamorphic rocks can be subdivided into
two main groups - _____________ and
_________________
• Groups are distinguished on the basis of:
–
–
–
, and
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Foliated Rocks
• Foliation (Latin root folium meaning ____),
refers to the _________________________
in a metamorphic rock
• Individual layers range from 0.1 mm to > 1
m in thickness
• Foliated rocks display a distinctive _______
or __________ appearance
• Foliation allows samples to be ___ into thin
sheets
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Foliated Rocks
• Foliation results from:
– 1)
or
– 2)
• Foliated rocks are distinguished on the basis
of:
•
•
•
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Metamorphic Rocks # 2
9/28/2005
Foliated Rocks
• Examine the characteristics of various
common foliated metamorphic rocks
–
–
–
–
–
–
slate
phyllite
schist
amphibolite
gneiss
migmatite
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Foliated Rocks - Slate
• Results from the
metamorphism of ______
under very low ________
and ___________ in
response to pressure
solution and
________________
• _______ _______ results
from the compression and
shearing of shale and
often forms at an ____ to
the original bedding
Slaty Cleavage
Original Bedding
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Foliated Rocks - Slate
• foliation developed is termed slaty cleavage,
reflecting the _________ __________ of clay
minerals
• slate can be split easily along cleavage planes
into thin sheets used for roofing tiles, floors,
pool tables
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Metamorphic Rocks # 2
9/28/2005
Foliated Rocks - Slate
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Foliated Rocks
• Metasandstone and Metaconglomerate
– sandstone and conglomerate occur __________
with shale
– subjected to the same metamorphic conditions
that __________ shale to slate
– resulting in the development of a weak ______
defined by ________ ________ grains and
conglomerate ________, generally by _______
______________ and recrystallization
– prefix ‘meta’ added indicating that the original
sediment is recognizable and a foliation is
present
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Metasandstone
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Metamorphic Rocks # 2
9/28/2005
Metaconglomerate
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Foliated Rocks
• Phyllite
– root word for phyllite derived from Greek
phyllon meaning _____, indicating ____ layers
– ______________________________________
______________________________________
______________________________________
______________________________________
– display a ___________ lustre (silky sheen) due
to light reflecting off fg mica flakes
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Foliated Rocks
• Phyllite
– forms by heating slate such that clay minerals
recrystallize to micas
– ______________ may take place while the rock
is being sheared or squashed, with the resulting
mica flakes oriented perpendicular to the
direction of flattening
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Metamorphic Rocks # 2
9/28/2005
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Foliated Rocks
• Schist
– ______________________________________
______________________________________
______________________________________
______________________________________
– foliation is called _____________
– progression from phyllite to schist is gradual
– minerals other than ________ and _______ in a
schist may include:
• quartz, feldspar, garnet, staurolite, alumino silicates
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Metamorphic Rocks # 2
kyanite muscovite schist
garnet biotite schist
9/28/2005
biotite schist
Garnet muscovite schist
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Foliated Rocks
• Schist
– Naming a schist is based on the major minerals
present, listed in increasing order of abundance
– A schist may develop from ________ other
than shale, eg. greenschist - a green schist
developed through the metamorphism of a
mafic-rich rock - basalt.
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Metamorphic Rocks # 2
9/28/2005
Foliated Rocks
• Amphibolite
– ________ and ______ contain abundant MgO
and little SiO2, as such when they are undergo
metamorphism they do not produce ______ and
_______
– predominant mineral produced is amphibole
(______________) with __________, and may
or may not contain __________
– resulting ____ _______ rock is an amphibolite
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Foliated Rocks
• Gneiss
– ______________________________________
______________________________________
_________________________
– layering is the result of _____________ and
____________
– layers reflect ______________ content:
• light coloured - ________, ________, __________
• dark coloured - ________, ________, __________
– if a gneiss contains micas it may also display a
________________
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Metamorphic Rocks # 2
9/28/2005
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granitic gneiss
straight gneiss
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Foliated Rocks
• Migmatite
– at the ______ temperatures at which a gneiss
forms, a rock may undergo ______ ________
– under partial melting the first minerals to melt
out have _____ melting temperatures (quartz,
alkali feldspar and muscovite) and form a high
silica magma (________ composition) and
– leaves behind an ________ fraction (____) rich
in ________ minerals (amphibole, pyroxene,
biotite)
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Metamorphic Rocks # 2
9/28/2005
Foliated Rocks
• Migmatite
– result is a _______ _____ that does not migrate
great distances and __________ within the
local area
– resulting rock is a migmatite - a mix of ______
and __________ rocks that display
layers/pods/lenses of ‘granitic’ rocks which
grade into layers of relict gneiss
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Metamorphic Rocks # 2
9/28/2005
Non-Foliated Rocks
• Non-foliated metamorphic rocks are those
that contain minerals produced as a result of
metamorphic _______________ but do not
display a ____________
• Minerals are _________ oriented and do not
normally develop a _______/__________
• The rocks are _________ in nature
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Non-Foliated Rocks
• Hornfels
– rocks which undergo ________ metamorphism
due to the __________ of an igneous body are
subjected to an _______ in _________ without
being subjected to any _________
– resulting non-foliated metamorphic rock is a
hornfels, characterized by _____, ________
__________________
– specific minerals present are dependant on the
________ composition and the ___________ at
which the metamorphism takes place
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Non-Foliated Rocks
• Quartzite
– quartz sandstone consists of ________ _______
________ grains ________ together
– in response to metamorphism _______ and
_________ recrystallize producing a massive
quartzite
– new grains of quartz form an __________
________ effectively _________ together
– quartzite appears _______ than sandstone due
to recrystallization
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Metamorphic Rocks # 2
9/28/2005
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Quartz Sandstone to Quartzite
Sandstone
Quartzite
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From: Marshak 2001
Non-Foliated Rocks
• Marble
– metamorphism of ________, or ________-rich
rocks, yields a marble
– in response to metamorphism the calcite in the
original limestone ______________ into an
interlocking ______ of ______ calcite grains
– any original _________ features - fossils, pore
spaces, fine scale layering, etc., in the limestone
are ___________ recognizable
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Metamorphic Rocks # 2
9/28/2005
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Identification of Metamorphic Rocks
massive to weakly
foliated, vfg, dark green
Aphanitic
Greenstone
(Volcanic Rock)
Textural terms indicated in italics
hornblende
Amphibolite
(mafic rocks)
calcite
Marble
(limestone)
dolomite
Marble
(dolostone)
Mineral names are underlined
Rock names indicted in bold
Quartzite
quartz
Slaty Cleavage
Cleavage surface dull to
shiny, minerals defining
foliation vfg
(quartz
sandstone)
Slate
platy, needle
shaped grains
producing the
foliation
Grain Schist
(shale, poorly
sorted sandstone,
volcanic rocks)
(shale, volcanic rock)
porphyroblastic
Foliated
Protolith compositions in (parenthesis)
Mineralogy
Begin Here
Crystalline
identify mineral, add
prefix to rock name
mixture of biotite
and muscovite
producing foliation
Schistosity
non-porphyroblastic
quartz, feldspar,
micas, hornblende
Gneissosity
biotite major dark
mineral
hornblende major
dark mineral
mostly muscovite
producing foliation
Mica Schist
(shale, volcanic
rocks)
Muscovite
Schist
(shale)
Gneiss
(shale, poorly sorted
sandstone, granitic rocks)
mostly biotite
producing foliation
Biotite Schist
(shale, volcanic
rocks)
Biotite Gneiss
(shale, poorly sorted
sandstone, granitic rocks)
Hornblende Gneiss
(volcanic, granitic rocks)
mostly hornblende
producing the
foliation
Hornblende
Schist
( volcanic rocks)
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