Earth Materials Unit: Metamorphic Rocks
and Processes
Text: Chapters 7
Lab: Laboratory 7
Name________________________________
Geology 12: Metamorphic Rocks
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Metamorphic Rocks and Processes
Purpose: To classify metamorphic rocks and features by their
physical and chemical properties.
-By the end of this unit, students are expected to be able to:
1. Relate the types and characteristics of metamorphic rocks to:
a) Parent Rock
b) Temperature
c) Pressure
d) Chemical Conditions
2. Describe the features of, and identify, the following sedimentary rocks:
Slate
Phyllite
Quartzite
Marble
Schist
Gneiss
Metaconglomerate
3. Contrast the two major categories of metamorphic rocks:
a) Foliated
b) Non-foliated
4. Contrast the two types of metamorphism:
a) Contact
b) Regional
5. Describe changes that occur in country rock and in the intrusion at a contact region.
6. Relate metamorphic rock type to the concept of metamorphic grade.
Geology 12: Metamorphic Rocks
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Geology 12: Metamorphic Rocks and
Processes
Part A: What is a Metamorphic Rock?
Rocks that have changed from one form to another through the addition
of intense heat, pressure or fluid activity.
Part B: Agents Metamorphism
The chemical composition of a metamorphic rock is determined by its
parent rock (protolith), but its texture and mineral makeup depends on
the agents of metamorphism that acted on it.
Heat
Heat can be added to rocks by:
a) ________________________________________________________
b) ______________________________________________________
Heat causes recrystallization (not melting!) to form equigranular
crystals, like marble.
Heat changes the distribution of the chemical components of the rock.
*Remember that minerals are stable at different temperatures!
Pressure (Stress)
a) Confining Pressure
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Increases with burial at depth and can cause mineral grains to compact
together. This forms a harder/denser rock, but has little impact on the
internal structure of the rock.
b) Directed Pressure
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There are three types of directional pressure:
i) Compression: Pushing together; ii) Tension: Pulling apart; iii) Shear Parallel forces
Geology 12: Metamorphic Rocks
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At high enough temperatures where rocks are ductile, highly folded strata and
foliation can be produced.
Foliation: ________________________________________________________
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Chemically Active Fluids
Water and other volatiles become reactive when heated and act as catalysts to
cause metamorphism.
Heated fluids dissolve ions from minerals from regions of high stress and deposit
them in regions of low stress. This allows minerals to grow longer in the
direction perpendicular to compressional stress (produces foliation).
Heated fluids can cause chemical changes in porous rocks and also transport
chemicals from one area to another where they can produce more minerals.
Will metamorphic rocks altered by fluids have the same chemical composition as
their parent rocks?
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Metamorphic Grade
Metamorphic Grade is the amount
of metamorphism (heat, pressure,
fluid activity) a rock has
undergone.
Metamorphic grade can be
indicated by index minerals which
only form at specific temperatures.
What grade did a rock containing
garnet form?
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The amount of heat and pressure put onto a rock varies depending on the scale of metamorphism:
Burial Metamorphism
Alteration of rock by an increase in temperature (geothermal gradient) and confining pressure caused by
the weight of overlying sediment/volcanic layers.
Mild metamorphism, rock becomes denser but previous features are preserved (e.g. bedding, grain size)
Geology 12: Metamorphic Rocks
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Contact Metamorphism
Igneous intrusion bakes the immediately surrounding
rocks, forming aureoles (altered zone around the
intrusion). Usually only a small (km’s) area is affected.
The addition of heat without pressure creates unfoliated
rocks with random crystal orientation.
Heat decreases with distance from the intrusion,
creating rocks with high metamorphic grade next to the pluton and then lower grades as you move
outwards.
What type of rocks are often formed closest to the igneous intrusion? (Lab page 156)
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Regional Metamorphism
Metamorphism on a large scale, caused by pressure,
heat and fluid activity. It is the most common type of
metamorphism and is associated with convergent plate
boundaries.
Index minerals, foliation and changes in texture are
common.
Metamorphic Rock Textures
Metamorphic rocks are divided into two groups:
a) Foliated
-Folaited rocks vary in their characteristics depending on the degree of metamorphism they underwent.
Define the foliated textures below using pages 159-161.
Slaty Rock Cleavage ___________________________________________________________________
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Phyllite ______________________________________________________________________________
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Geology 12: Metamorphic Rocks
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Schistosity ___________________________________________________________________________
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Gneissic Banding______________________________________________________________________
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b) Non-Foliated
-Nonfoliated rocks do not have obvious layering, but can be distinguished by other characteristics (Lab
pages 161-162):
Crystalline ___________________________________________________________________________
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Microcrystalline _______________________________________________________________________
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Sandy _______________________________________________________________________________
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Glassy _______________________________________________________________________________
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c) Some textures are common to both foliated and nonfoliated rocks. Define the following terms using
lab text page161-164:
Stretched Grains _______________________________________________________________________
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Geology 12: Metamorphic Rocks
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Porphyroblastic _______________________________________________________________________
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Hydrothermal Veins ____________________________________________________________________
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Folds _______________________________________________________________________________
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Lineations ____________________________________________________________________________
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*Complete Activity 7.1, 7.2 and 7.3
Geology 12: Metamorphic Rocks
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