GEOLOGY STUDY GUIDE
Module exam GL1 June 2004
METAMORPHISM
Geology Department, Greenhead College, Huddersfield.
Thin section of garnet mica schist x 10 magnification
Your name .....…………………….................................................
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Date
LEARNING TARGETS
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notes
When you have completed this study guide, you will:
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Be able to define metamorphism
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Recognise the main metamorphic rocks
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Know the difference between contact and regional metamorphism
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Recognise and understand metamorphic minerals
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Be able to draw diagrams to show metamorphic textures in
microscope thin section
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Have tested your knowledge in a variety of ways.
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GEOLOGY STUDY GUIDE
Module exam GL1 June 2004
Resources
Here is a choice of resources to use. You do not need to look at them all but clearly the more
you read the better your knowledge of case studies will be. Tick the box once you have used
the resource.
If you read a photocopied extract then highlight it to help you reread it for revision. If you make
notes from a video tape make sure that the notes are headed with the name of the tape so that
you know the source of your information.
Understanding Geology David Webster p 80-85
 MET1
Geoscience Edwards and King p 124-134
 MET2
Geological Science by Andrew McLeish p 139-145
 MET3
Specification notes
 MET4
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Websites
www.geolsoc.org.uk/ Go to Teaching Resources
www.science.ubc.ca/~geol202
www.geologyshop.co.uk/metamo~l.htm
www.brookes.ac.uk/geology/8361/1998/freya/met.html
There are other websites you could search.
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ACTIVITY 1
TASK 1
DEFINITION
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Module exam GL1 June 2004
Read MET 1 p 80 and MET 4.
1. What is given as a definition of metamorphism?
2. Where in the crust will rocks be under greatest pressure?
3. What happens to the minerals in rocks when they are subjected to heat and/or
pressure?
4. If clay is heated in the sun to make a brick is it being metamorphosed?
5. If clay is heated in a kiln to 1400oC to make a brick is it being metamorphosed?
6. What happens to the texture of rocks when they are subjected to heat and/or
pressure?
The specification uses the definition below. Write it out on plain paper and define
all the words and phrases. Decorate to taste to help you remember the definition.
Metamorphism is the solid-state recrystallisation of pre-existing rocks in
response to changes in temperature and/or pressure. There can be changes in
texture and mineralogy of metamorphic rocks.
Use this box for notes
TASK 2 SOLID STATE RECRYSTALLISATION
The term we use for the process of metamorphism is solid state recrystallization.
“Recrystallization of the minerals in the original rock does occur but it is not total
recrystallization. Some of the crystals may melt, particularly where they are in
contact with other crystals under pressure. Most crystals remain in a solid state but
take up a different shape. Elements and ions are able to be mobilised as the rock is
heated and may be able to move into new crystal lattices which will produce
minerals of different compositions. What is important is that new minerals may
develop without the addition of new chemical elements.”
Draw diagrams to show what you understand by this paragraph.
Use this box for notes
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ACTIVITY 2 : CONTACT METAMORPHISM
TASK 3
METAMORPHIC AUREOLES AND BAKED MARGINS
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Module exam GL1 June 2004
Read MET 1 p 81 and MET 4 on contact metamorphism. Answer these questions:
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Define a metamorphic aureole.
Explain how it can form.
Draw a diagram of your own to show the effect of heat only on surrounding
country rocks. How can you show in your diagram that the effect of heat is
greatest on rocks close to the pluton?
Small igneous intrusions such as dykes and sills are not hot enough to have a
large-scale effect on country rocks. Draw a diagram of your own to show
how baked margins are formed.
TASK 4 EFFECTS ON SANDSTONE AND LIMESTONE COUNTRY ROCKS
How does the heat from the pluton change limestone and sandstone?
Draw diagrams to show the textural changes as these rocks are metamorphosed to
marble and metaquartzite.
TASK 5 PELITIC ROCKS – SHALES - MUDROCKS
Pelitic is a term used in metamorphic geology for any rocks originally made from
clay particles. New minerals are likely to develop if pelitic rocks are
metamorphosed because the chemistry of clays is complex and they are chemically
reactive.
In class we will explain the formation of spotted rocks and hornfels and their
characteristic minerals, chiastolite, and cordierite.
Use this box for notes
ACTIVITY 3 : REGIONAL METAMORPHISM
TASK 6 WHERE DOES REGIONAL METAMORPHISM TAKE PLACE?
Read MET 4 and other resources. Make a brief note to remind yourself about
which parts of the earth’s crust are likely to be under particularly high pressures
and so cause crustal rocks to change even though temperatures are not hot enough
for the rocks to melt.
TASK 7 METAMORPHIC TEXTURES
Use MET 4 as reference for this section. We can see that pressure and tension
have an effect on the alignment of minerals during regional metamorphism. The
texture that results is called foliation. There are three main types of foliation. In
class we will draw diagrams to illustrate all three – slaty cleavage, schistosity and
gneissose banding - and relate them to their characteristic rock lithology.
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TASK 8 INDEX MINERALS IN PELITIC ROCKS
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As temperatures and pressures increase, new minerals are formed from the clay
particles in pelitic rocks. Ions in crystal lattices of minerals are able to migrate and
form different minerals even though no new elements are added from outside.
Each mineral is characteristic of a particular temperature and pressure equilibrium.
If geologists can identify these index minerals in metamorphic rocks they can say
what the temperature/pressure conditions were when that rock was formed. We
use the phrase high grade for minerals found in rocks which have reached high
pressures and temperatures and low grade for those that have not been subjected to
such high temperatures and pressures.
Look at specimens of the regional metamorphic minerals – chlorite, biotite,
garnet, kyanite and sillimanite – to help you remember the order in which they
form.
Read MET 4 on Metamorphic Minerals and create a poster or diagram which will
help you learn the order of the index minerals.
Use this box for notes
ACTIVITY 4 : LEARNING METAMORPHISM
TASK 9 PRACTICAL
There are 6 main metamorphic rocks – spotted rock, slate, schist, gneiss, marble,
hornfels – that you need to be able to recognise in a practical exam.
Fill each practical sheet with a labelled pencil drawing to scale of a specimen of
each of these rocks. Note how hard the rock is, because of its crystalline nature.
Say whether you think that each rock is produced by heat or pressure or both.
You will probably be unable to recognise by tests and observations any of the
minerals because they usually are too small for you to identify them even with a
lens. Some rocks may have porphyroblasts. These are new crystals produced by
the metamorphic process, which are larger that the average size of the crystals.
Nevertheless you may need a lens to see them. Comment on the size of the
crystals, the alignment (if any) and the colour of the rock. Check the composition
with acid.
Margin notes
TASK 10
COMPOSITION OF THE MAIN METAMORPHIC ROCKS
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GEOLOGY STUDY GUIDE
Module exam GL1 June 2004
Match each composition below with the metamorphic rocks you have described in
Task 9.
a)
b)
c)
d)
e)
f)
Pale or dark, flaky mica minerals in layers giving the rock a shiny
appearance
White or grey coarsely crystalline rock which may have coloured streaks
and will fizz with dilute hydrochloric acid.
Any rock with spots or crystals randomly arranged
Extremely hard, finely crystalline rock often segregated into fine bands
Grey, purple or green rock made of very fine clay particles which have been
aligned so that the rock breaks along flat planes
Hard, coarsely crystalline rock divided into different coloured bands of pale
and dark minerals.
TASK 11 MICROSCOPE THIN SECTIONS OF METAMORPHIC TEXTURES
In class we will look at slides of rocks in thin section. The texture of metamorphic
rocks allows geologists to understand the conditions of heat and/or pressure that
the rock formed under. Be prepared to draw diagrams to show these metamorphic
textures. Have your sharpened pencil, compass and ruler ready.
TASK 12 WHY IS METAMORPHISM SO DIFFICULT TO LEARN?
Suggest reasons in your group and make a list of the main difficulties. Then look
at Fig 8.11 in MET 1 p 85. Explain why the diagram could be misunderstood.
Make sure that you understand what it means by explaining it to a friend.
Deadline for test on metamorphism…………………………………..
TASK 13 TEST YOURSELF
Complete MET 1 Questions 1 – 9 p 86-87
Deadline………………………………………..
TASK 14 EXAM QUESTION PACK
Complete the Metamorphic Rock EQP
Deadline: ………………………………………
TASK 15
REVIEW NOTES
You need to learn this topic now.
Review notes deadline: …………………………………….
Use this box for notes
ESTA GEOTREX The Geology Teachers Resource Exchange
Contributor: Alison Quarterman Establishment: Greenhead College Date:May 05
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