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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 years2. 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: non-continuous “layering” due to mineral alignment perpendicular to pressure
What are the metamorphic textures?
1. Slatey cleavage – tendency of fine-grained 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 Sheen Sparkly Layers (Dull)
What are the Non-foliated Metamorphic Rocks?
Quartzite – metamorphosed sandstonesandstoneVery hard
What are the Non-foliated Metamorphic Rocks?
Marble – metamorphosed limestoneFizzes 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 MetamorphismPressure 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 somethinga. 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 identif y all seven rocks
I. Answer questions A – D for all 7 rockspecimensA. Is the rock foliated or not?B. Describe the distinguishing properties of each
rock, especially metamorphic textures. (Howwould you recognize another specimen of thesame rock?)
C. Give the rock name.D. What kind (name) of rock was this before it
was metamorphosed?
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II. Put the foliated specimens in order ofincreasing metamorphism.Least heat and pressure a. ____ ___ ___ ___ ___
b. ____ ___ _____ ___ _
c. ____ _____ ___ ___ _
d. __ _____ ___ ___ ___
III. Read pages 49- 53 in the plum Tarbuck bookAnswer questions 12-15 on pages 57.
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