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Remember, “metamorphism” literally means to change form
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But what changes about the original parent rock?
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The size, the shape, the texture, and even the chemistry of the minerals can change!
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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

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What is it that can cause these rocks to change so drastically?
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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)

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Do all rocks get changed the same amount or the same way?
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No: It’s a sliding scale, much like many other things in geology
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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

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There are 3 types of metamorphism:
2.
3.
1.
Burial Metamorphism
Contact Metamorphism
Regional 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

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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

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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

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The texture of a metamorphic rock can be classified
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But unlike an igneous rock, there are only 2 types of texture
2.
1.
Foliated Texture
Non-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

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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

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We 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

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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

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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

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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

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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

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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

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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

Metamorphic
Rock Name
Slate
Schist
Parent
Rock
Shale
Slate
Gneiss Granite
Marble Limestone
Quartzite Sandstone
Anthracite Bit. Coal
Grade of
Metamorphism
Low
High
Very high
Low-Med
Med-High
High
Foliated or
Non-Foliated
Foliated
Foliated
Foliated
Non-Foliated
Non-Foliated
Non-Foliated

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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!