Metamorphic Rocks
What is a metamorphic rock?
Rocks in which minerals, texture and/or
structures have been changed by heat
and/or pressure
Conditions for metamorphism
Temperature
Pressure
Chemically active fluids
What is the relationship between
temperature & Metamorphic Rock?
1. Below 200°C – rocks are stable for
millions of years
2. 200 - 600°C – still below melting point
(solid) but some atoms are able to move
around and rearrange
3. Above 600°C – minerals begin to melt
(form igneous rocks)
How does pressure make a
metamorphic rock?
About 1 mile to 25 miles deep – vertical
pressure from overlying rocks
How does pressure make a
metamorphic rock?
Along continental
margins – due
to mountain
building forces
(horizontal
pressure)
How are chemically active fluids
used to make metamorphic rocks?
Water in pore spaces aids in atomic
movement
What results from
metamorphism?
Same amount of mass
squeezed into a
smaller volume,
density increases
Spaces between rocks
(cracks, etc.) are
squeezed shut,
porosity decreases
What results from
metamorphism?
Existing
crystals
become
aligned
perpendicular
to pressure
What results from
metamorphism?
New minerals are
formed because
atoms have
different
“comfortable
position” under
new temperature
and pressure
conditions
Metamorphic Textures
Foliation: noncontinuous
“layering” due
to mineral
alignment
perpendicular
to pressure
What are the metamorphic
textures?
1. Slatey cleavage – tendency of finegrained rock to split along foliation
planes (not necessarily coincident with
stratification)
What are the metamorphic
textures?
2. Schistosity – visible parallel crystals of
mica, chlorite, or talc
What are the metamorphic
textures?
3. Gneissic layering – alternating light and
dark minerals
What are the metamorphic
textures?
Non-foliated: single mineral rocks have
crystals that grow equally in all
directions
Examples:
Quartzite
Marble
What are the foliated
metamorphic rocks?
1. Slate – metamorphosed shale or an
extrusive igneous rock
Dull looking - Platy
What are the foliated
metamorphic rocks?
2. Phyllite – shiny surface on foliation
planes, micro-crystals began to develop
Sheen
What are the foliated
metamorphic rocks?
3. Schist – visible parallel crystals of mica
Looks sparkly
What are the foliated
metamorphic rocks?
4. Gneiss – alternating bands of light and
dark crystals
What are the foliated
metamorphic rocks?
Granite
Shale  Slate  Phyllite  Schist  Gneiss
Smooth
Platy
(Dull)
Sheen
Sparkly
Layers
What are the Non-foliated
Metamorphic Rocks?
Quartzite – metamorphosed sandstone
Very hard

What are the Non-foliated
Metamorphic Rocks?
Marble – metamorphosed limestone
Fizzes with acid

What are the Non-foliated
Metamorphic Rocks?
Metaconglomerate/metabreccia – rock
breaks through instead of around clasts
Examples:
Metaconglomerate
Metabreccia
What are the types of
metamorphism?
Regional metamorphism

Contact
Metamorphism

Regional Metamorphism
Pressure from force
colliding crustal
plates
Temperature raised by
compression,
friction, and
movement inward
toward interior
Associated with linear
mountain chains
Contact Metamorphism
Results from physical
contact with something
a. magma or lava (high
temperature, low
pressure)
b. meteorites (low
temperature, high
pressure)
Contact Metamorphism
Small scale
Pressure due to
gravity, any
foliation which
forms is usually
horizontal
Where rocks
form
determines
what kind
of rock
will be
produced.
Rock Cycle
Rock Cycle
Metamorphic Rock Lab
Use your dichotomous key to identify all seven rocks
I.
Answer questions A – D for all 7 rock
specimens
A. Is the rock foliated or not?
B. Describe the distinguishing properties of each
rock, especially metamorphic textures. (How
would you recognize another specimen of the
same rock?)
C. Give the rock name.
D. What kind (name) of rock was this before it
was metamorphosed?
************************************************************************
II. Put the foliated specimens in order of
increasing metamorphism.
Least heat and pressure 
a. ________________
b. ________________
c. ________________
d. ________________
III. Read pages 49-53 in the plum Tarbuck book
Answer questions 12-15 on pages 57.