Download Metamorphic Rocks

METAMORPHIC
ROCKS
Rocks of Change
The Keys to Metamorphic Rocks
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Remember, “metamorphism” literally means to
change form
But what changes about the original parent rock?
The size, the shape, the texture, and even the
chemistry of the minerals can change!
Which kind of rocks can be changed into a
metamorphic rock? All Types:
– Igneous rocks can be changed
– Sedimentary rocks can be changed
– Even metamorphic rocks can be changed into other
kinds of metamorphic rocks
Meta-why?
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What is it that can cause these
rocks to change so drastically?
Three factors:
1. Pressure from deep burial
2. Heat from deep burial or a nearby
magma body
3. Chemically active fluids percolating
through the rock (we don’t get into this)
Meta-how much?
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Do all rocks get changed
the same amount or the
same way?
No: It’s a sliding scale,
much like many other
things in geology
Low-grade metamorphism
– hardly changed from the
original parent rock
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High-grade metamorphism
– cannot even recognize the
original parent rock
The hotter and deeper the
rocks go the greater the
metamorphism will be
Different types of Change
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There are 3 types of metamorphism:
1.
2.
3.
Burial Metamorphism
Contact Metamorphism
Regional Metamorphism
Burial Metamorphism
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Burial
Metamorphism –
usually a low grade
change due to
pressure caused by
shallow to medium
burial; heat is not
a major factor
Burial Metamorphism will
not drastically change the
parent rock
Contact Metamorphism
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Contact Metamorphism – also usually a
low grade change; the parent rock comes
in contact with a magma body and gets
cooked enough to metamorphose
Contact
Metamorphism
Rising magma bodies will metamorphose nearby rocks
Regional Metamorphism
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Regional Metamorphism – both heat and
pressure change rock on a grand scale;
this usually occurs during major tectonic
events such as mountain building
Regional
Metamorphism
The highest grade of change will occur during regional metamorphism
Texture You Say?
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The texture of a metamorphic rock
can be classified
But unlike an igneous rock, there
are only 2 types of texture
Foliated Texture
Non-Foliated Texture
1.
2.
Foliated Texture
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In Foliated rocks
mineral grains align
parallel because of the
pressure & heat
This recrystallized
mineral alignment
causes the rock to
have a banded look
Rocks with multiple
mineral types will
exhibit this texture
Notice the foliation of
this gneiss sample
Non-Foliated Texture
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In Non-Foliated rocks
the minerals do not
line up parallel
These rocks have a
uniform appearance
and no banding
Rocks that have only
one kind of mineral
will usually exhibit this
metamorphic texture
No mineral alignment
Non-Foliated rocks do not
have banding in them
Naming & Classifying
Metamorphic Rocks
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can group these into the two
categories based upon the types of
texture the rocks exhibit
Foliated Rocks
•Slate
•Schist
•Gneiss
Non-Foliated Rocks
•Marble
•Quartzite
•Anthracite
Naming Foliated Rocks
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Slate – a low grade
metamorphism of the
parent rock shale
The thin platy mica
flakes line up and give
the rock foliation
Slate has great “rock
cleavage” and it used
as roof & floor tile,
chalkboards, and
billiard table tops
Slate is a low grade
metamorphic rock which
was once used as hand held
chalk boards in schools
Naming Foliated Rocks
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Schist – higher grade
metamorphism of the
rock slate
Schist is “platy” due to
the mica minerals,
and it can be split into
flakes & slabs
Schist is a high grade
metamorphic change
Schist is a high grade
metamorphic rock with
obvious foliation
Naming Foliated Rocks
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Gneiss (“nice”) – A
foliated rock from the
parent rock granite
Minerals are banded,
but instead of being
platy like schist, they
are granular and
rounded
Gneiss is a very high
grade metamorphic
change
Notice the good
foliation in this
sample of gneiss
Naming Non-Foliated Rocks
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Marble – coarse
grained crystalline
rock from the parent
rock limestone
It has large crystals of
interlocking calcite
Calcite has a hardness
of 3 so it is relatively
soft and great for
carving and sculpting
Marble is a low-med
metamorphic change
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The calcite crystals
that make up
limestone do not
change drastically
when marble is
made; if anything,
they will grow in
size as they fuse
together
Naming Non-Foliated Rocks
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Quartzite – very hard
rock made from the
parent rock sandstone
With heat/pressure
the quartz grains
simply fuse together
Quartzite is a
medium-high grade
metamorphic change
The rock quartzite is
not too different than
a large quartz crystal
Naming Non-Foliated Rocks
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Anthracite – the
highest grade of coal
It forms from the
continued cooking of
bituminous coal
Anthracite is a high
grade metamorphism,
it is extremely hard,
and it burns almost
completely clean
Both of these anthracite
samples are hard and shiny
Naming Metamorphic Rocks
Metamorphic
Rock Name
Parent
Rock
Grade of
Metamorphism
Foliated or
Non-Foliated
Slate
Shale
Low
Foliated
Schist
Slate
High
Foliated
Gneiss
Granite
Very high
Foliated
Marble
Limestone
Low-Med
Non-Foliated
Quartzite
Sandstone
Med-High
Non-Foliated
Anthracite
Bit. Coal
High
Non-Foliated
To Review:
All aspects of a rock
can change during
metamorphism
 All rock types can
undergo metamorphism
 Heat, pressure, and
fluids do the changing
 There are three types
of metamorphism: burial,
contact, & regional
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There are two types
of textures in
metamorphic rocks:
foliated & non-foliated
 Foliated rocks look
banded due to mineral
alignment
 Non-foliated rocks do
not look banded
 Learn the six rocks!
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