| at least to give an opportunity(of) (-., -.) In sucha way 21. ) ( ), . : known unknown; differ different difference; found founder foundation; mean meaning; difficult difficulty ) -able: changeable, understandable, valuable, variable, breakable ) , : 1. Under the action of pressure and high temperature rocks change their composition and structure. One may say that the structure and composition of rocks are.... |
band [btend] ; ; (); syn layer
cleave [kli:v] v ; - , ; cleavage n
constituent [kan'stitjusnt] ,
define [di'fain] v ,
[dis'tnbjurt] v (among) (); s'ta:b] v ;
excess [ik'scs] , ; ant deficiency [di 'fi/(s)nsi]
flaky ['fleiki] ;
fluid [ 'flu(:)id] ;
foliate [Toulieit] v ; foliated , ; syn flaky
marble [ 'ma:bl]
mention ['/()] v , ;
plate [pleit] n ; ()
pressure ['/] ; rock pressure (underground pressure) ,
relate [ri'leit] v ; ; related ; relation ; relationship ; ; relative ;
run [] (ran [ran], run) v , ; ; ( ); , ; (); (, )
schistose ['Jistous] a ;
sheet |Ji:t]
slate [sleit] ; syn shale
split [split] (split) v , , ; syn cleave
trace [treis] ; tracing
126______________________________________________ Unit 5
2. Everybody understands that metamorphic rocks have been
developed from earlier igneous and sedimentary rocks. It is quite...
that these changes take place in texture, in mineral composition and
in structural features of rocks.
3. Soft rocks can break into pieces. They are....
4. Rare metals are of great value. They are very....
5. Rock pressure and temperature vary. The role of water in
metamorphism is determined by four... parameters.
22. ,
-1.
chief chiefly..., general , generally..., common commonly..., original originally..., particular particularly..., practical , practically..., usual usually..., wide widely...
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23. . :
cleavage distribution the definition of rocks
geological disturbances schistose structure
schistose coal low-grade metals
medium-grade coals high-grade oil
the most common metamorphic exposed igneous rocks
rocks single oithoclase crystals
chemically active fluids scientific value
rock pressure water pressure
excess of water thin sheets
foliated and non-foliated the Earth's surface
metamorphic rocks separate plates
24.
:
metamorphic rocks; some changes in texture; in mineral composition and structure; the description of metamorphism; schistose structure; the role of water; four variable geologically related parameters; flaky materials; the mechanism of metamorphic deformation; crystalline schists; the great dislocations of the Earth's crust; during normal progressive metamorphism
25. :
1. What is metamorphism?
2. Why can metamorphic rocks cleave easily?
3. Why is the study of metamorphic rocks important?
Unit 5__________________________________________ 127
Metamorphic Rocks
The problem discussed concerns metamorphic rocks which compose the third large family of rocks. "Metamorphic" means "changed frop". It shows that the original^ rock has been changed from its primary form to a new one. Being Subjected to, pressure, heat and chemically active fluids beneath the Earth's surface, various rocks in the Earth's crust rundergo changes in texture, in mineral corhpositioh and structure and are transformed into meta-morphic rocks. The process describeci is called metamorphism.
As is known, metamorphic rocks have been developed from ear
lier igneous and sedimentary rocks by the action of heat and pressure.
^ Gneisses, mica schists, phyllites, marries, slate, quartz, etc.
belong to the 7sarhe group of rocks, ija'yirijj the same mineral cdni-
position as granite, gneisses consist chiefly of quartz, orthoclase
andl mica^. However uhMe granite, they have a schistose structure. It
rtfeans tjjat their constituents are Aisfnbutejdf in bands or layers and
rar^ parallel to each other in one'Direction. If 4|sjturbed jhe rock
Cleaves easily into separate plates.
The role of water in rnetamorphism is deterrnine^ by at least four v^riaDle'geologically refuted parameters: rock pressure, tempera-
ture.water pressure, and the am'oimt of water present.
? During a normal progressive metamorphism rock pressure and temperature are iriterciependent, and the amount of water and the pressure of water arejrela|e<! ?t^ the sediments and to the degree of metamorphism in'such a^way'tfiat, gerienBry. speaking, the low-grade metamorphic rocks are characterized by the excess of water. The medium-grade rocks defined by some deficiency of water and the high-grade metamorphic rocks are characterized by the absence of water.
Many of the metamorphic rocks -mentioned above consjst,of flaky materials such as mica and chlorite. These minerals cause the' rock to split into thin sheets, and rocks become foliated. -
Slate, phyllite, schist and gneiss belfcng to the group of foliated
metamorphic rocks. Marble and quartzite are non-foliated metamor
phic rocks,
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The structure of nietamo,rphic rocks is of importance because it shows the nature of i>re-existmg j;ocks and the mechanism of metamorphic deformation. Every trace ofc/6nginal structure is of great importance to geologists. It gives an opportunity of analysing the causes of its metamorphism.
128______________________________________________ Unit 5
Being often called crystalline schists, metamorphic rocks such asi gneisses and mica have a schistose structure. Metamorphic rocks represent the oldest portion of the Earth's crust. They are mostly found in the regions of mountain belts where great dislocations on the Earth once took place.
26. , .
.
1. Generally speaking, metamorphic rocks have been developed
from ores.
2. Marble, slate and phyllite belong to the group of metamor
phic rocks.
3. As is known, unlike granite metamorphic rocks have a schis
tose structure.
4. It is quite obvious that the role of water in metamorphism is
great.
5. As a rule, low-grade metamorphic rocks are characterized by
the absence of water.
6. Flaky materials cause the rock to split into thin sheets.
7. It should be noted that marble and quartzite are foliated
metamorphic rocks.
8. The structure of metamorphic rocks shows the nature of older pre
existing rocks and the mechanism of metamorphic deformation as well.
9. All metamorphic rocks are non-foliated.
27. :
1. Do you know how metamorphic rocks have been formed?
2. Which rocks belong to the group of metamorphic?
3. Does gneiss have the same structure as granite?
4. Is the role of water great in metamorphism?
5. What rocks do we call foliated? What can you say about non-
foliated metamorphic rocks?
6. How can geologists trace the original structure of metamorphic
rocks?
7. Why are metamorphic rocks often called crystalline schists?
28. i)
:
1. as a result of the chemical ) ( )
and physical changes )
2. constituents of rocks )
Unit 5
3. to be subjected to constant
development
4. to undergo changes
5. excess of water
6. low-grade ores
7. coal band
8. to cleave into separate layers
9. traces of original structure
10. generally speaking
)
)
)
)
)
) )
) :
| 1. 2. 3. 4. 5. 6. 7. 8. 9. |
| 10. 11. |
) unlike granite
) to be of importance
)
r) mentioned above
) schistose structure
) to give an opportunity (of doing
smth)
) to define (determine) rock texture
) deficiency of water
) flaky rocks
) marble and slate ) gneiss
29. , :
cleave cleaves cleavage
1. Metamorphic rocks which have a schistose structure can....
2. As a result of splitting... is formed.
3. Generally speaking, the constituents of gneisses are distributed
in bands or layers and the rock... easily.
