1. a) sandstone
2. ) fine-grained sand
3. ) the Earth's crust
4. ) exposed rocks
5. ) to dissolve in water
6. ) like gypsum
7. ) consolidated sediments
8. ) igneous rocks
9. ) to solidify, to consolidate
) .
1. coarse-grained sand )
2. siltstone and shale )
3. the destructive action of water )
4. existing rocks ) (- )
5. chemical decay )
6. sedimentary rocks e)
7. stratified deposits )
8. pre-glacial period )
9. particles of a substance )
8
contain - v ( ),
crack - n ; ; v ; ,
contract - v ;
dust - n
expand - v ); () ; expansion ; ant contract
fissure - n ( , ); ;
fracture - n ; ; ; v (); ()
freeze - v ; ;
gradual - ; gradually adv
hard - , ; ant soft; ( ); adv , ; hardly adv ,
hole - n ; ; ;
influence - n ; v (on, upon) ( -.)
lateral -
occur - v ; ; ; syn take place, happen; occurrence - ; mode of occurrence -
penetrate - v (), (-.)
phenomenon - n ; pi phenomena
pressure - n ; lateral pressure () ; rock pressure ,
rate - n , ; , ; ; ; syn speed, velocity
refer - v (to) ( -.); ( , )
resist - v ; ; ; resistance - n ; resistant - ; ;
size - n ; ; ()
solution n ; soluble - ; solvent - ;
succession n , ; in succession
undergo (underwent, undergone) - v (-.), (-.)
uniform a ;
weathering - n ; (, ..)
to be subjected to
Weathering of Rocks
All rocks which are exposed on the Earth's surface (high mountain peaks, deserts) are decomposed to a certain degree. The process of rock disintegration by the direct influence of local atmospheric conditions on the Earth's surface is called weathering. This phenomenon is often referred to in geology because weathering is an active process. It takes place in the upper layers of the Earth's crust.
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The main cause of physical weathering is the change in temperature that takes place with the succession of day and night. This phenomenon can best be observed in the deserts and high mountains where the changes in temperature are common.
During the day under the influence of heat, rocks expand whereas at night they begin to contract. As rocks are generally composed of different minerals, their expansion and contraction do not occur uniformly. As a result of this rocks crack. At the beginning these cracks or fissures are hardly noticeable but gradually they become wider and deeper until the whole surface of rock is finally transformed into gravel, sand or dust.
In the regions of a moderate or cold climate, where the temperature in winter goes down to below 0 (zero), the decomposition of rocks is greatly facilitated by the action of water. When water freezes it increases in volume and develops enormous lateral pressure. Under the action of water, rocks decompose to pieces of varied forms and sizes.
The decomposition of rocks under the direct influence of heat and cold is called physical weathering.
Rocks are subjected not only to physical decomposition but also to chemical weathering, i.e. to the action of chemical agents, such as water, carbon dioxide and oxygen. In a general way, chemical weathering is an acid attack on the rocks of the Earth's crust, in particular an attack on the most abundant minerals quartz (sand) and aluminosilicates (clays). Only few minerals and rocks are resistant to the action of natural waters. The solvent action of water is stronger when it contains carbon dioxide. Water causes more complex and varied changes. With the participation of oxygen and carbon dioxide up to 90 per cent of rocks is transformed into soluble minerals, which are carried away by the waters.
Organisms and plants also take part in the disintegration of rocks. Certain marine organisms accelerate the destruction of rocks by making holes in them to live in. The action of plants can often be even more destructive. Their roots penetrate into the fissures of rocks and develop the lateral pressure which fractures and destroys rocks.
, . .
1. The process of sedimentation is called weathering.
2. The change in temperature causes physical weathering.
3. As a rule during the night rocks expand.
4. When freezing water decreases in volume and develops enormous lateral pressure.
5. The decomposition of rocks is due to the influence of heat and cold.
6. As a rule water contains dissolved mineral substances.
7. The solvent action of water is stronger when it does not contain carbon dioxide.
8. It should be noticed that the action of organisms and plants is destructive.
9. Certain marine organisms accelerate the destruction of rocks.
2. :
1. What process is called weathering?
2. What process is called physical weathering?
3. Where can the phenomenon of physical weathering be best observed?
4. What process is called chemical weathering?
5. What substances can act as solvents?
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6. Are all minerals and rocks resistant to the action of natural waters or only few minerals and rocks can resist the action of water?
7. How do organisms act on the destruction of rocks?
3. ) :
1. the Earth's surface
2. to be composed of different minerals
3. the expansion of rocks
4. changes in temperature
5. under the influence of heat
6. weathering
7. destructive forces
8. a great number of fractures
9. to penetrate into fissures
)
)
)
)
)
)
)
)
)
) :
1.
2.
3.
4.
5.
6. (-.)
7.
8.
9.
) to facilitate the decomposition of rocks
) to increase in volume
) to resist (smth)
r) rock pieces of varied (different) sizes
) to accelerate the process of weathering
) to be subjected to decay
) to dissolve substances
) to develop lateral pressure
) certain organic substances
9
abyssal - , ; hypabissal - a
adjacent - ,
ash - n
belt - n ; ;
body - n , ; solid (liquid, gaseous) bodies (, ) ; ; ; ;
common - ; ; syn general; ant uncommon
cool - v (); ; ; ant heat ()
dimension - n ; pl ; ; syn measurement, size
dust - n
dyke n
extrusion - n ; ; ant intrusion ; . ( )
fine - , ; ; ; ; , ( ); ; fine-graded (fine-grained) , ; fines - pl ;
flow - v ; ; n ; ; flow of lava
fragmentary - ,
glass - n ; glassy - , ;
gold - n
inclined -
mica - n
permit - v , ; syn allow, let; make possible
probably - adv ; syn perhaps, maybe
shallow - ; ; ant deep
sill - n ,
stock - n ,
vein - n , ,
Igneous Rocks
Igneous rocks have crystallized from solidified magma.
Igneous rocks can be classified in a number of ways and one of (hem is based on mode of occurrence. They occur either as intrusive (below the surface) bodies or as extrusive masses solidified at the Earth's surface. The terms "intrusive" and "extrusive" refer to the place where rocks solidified.
The grain size of igneous rocks depends on their occurrence. The intrusive rocks generally cool more slowly than the extrusive rocks and crystallize to a larger grain size. The coarser-grained intrusive rocks with grain size of more than 0.5 mm called plutonic or abyssal are referred to as intrusive igneous rocks because they are intruded into older pre-existing rocks. Extrusive or volcanic rocks have even finer grains, less than 0.05 mm and are glassy.
Exposed igneous rocks are most numerous in mountain zones for two reasons. First, the mountain belts have been zones of major deformation. Second, uplifts in mountain belts have permitted plutonic masses to be formed.
The largest bodies of igneous rocks are called batholiths. Batholiths cooled very slowly. This slow cooling permitted large mineral grains to form. It is not surprising that batholiths are composed mainly of granitic rocks with large crystals called plutons. As is known, granites and diorites belong to the group of intrusive or plutonic rocks formed by solidification of igneous mass under the Earth's crust. Granites sometimes form smaller masses called stocks, when the occurrence has an irregular shape but smaller dimensions than the batholiths.
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Laccoliths and sills, which are very similar, are intruded between sedimentary rocks. Sills are thin and they may be horizontal, inclined or vertical. Laccoliths are thicker bodies and in some cases they form mountains.
Dykes are also intrusive bodies. They range in thickness from a few inches to several thousand feet. Dykes are generally much longer than they are wide. Most dykes occupy cracks and have straight parallel walls. These bodies cool much more rapidly and are commonly fine-grained. For example, granite may occur in dykes that cut older rocks.
Pegmatites (quartz, orthoclase and mica) also belong to the group of plutonic or intrusive rocks. They occur in numerous veins which usually cut through other plutonites, most often granite, or adjacent rocks.
Extrusive igneous rocks have been formed from lava flows which come from fissures to the surface and form fields of volcanic rocks such as rhyolite, andesite, basalt, as well as volcanic ashes and dust, tuff, etc. As a rule, these rocks of volcanic origin cool rapidly and are fine-grained. It is interesting to note that basalt is the most abundant of all lavatypes. It is the principal rock type of the ocean floor.
Igneous rocks are rich in minerals that are important economically or have great scientific value. Igneous rocks and their veins are rich in iron, gold, zinc, nickel and other ferrous metals.
, . .
1. Igneous rocks have been formed by sedimentation.
2. Intrusive rocks have been formed by the cooling of rocks of the Earth's crust.
3. Extrusive rocks have been formed the same way.
4. The grain size of igneous rocks depends on mode of occurrence.
5. Exposed igneous rocks are numerous in mountain zones.
6. Granites and diorites belong to the group of extrusive rocks.
7. As a rule, granite may occur in dykes.
8. Pegmatites do not belong to the group of plutonic or intrusive rocks.
2). :
1. Have igneous rocks crystallized from magma or have they been formed by sedimentation?
2. Which types of igneous rocks do you know?
3. What does the grain size of igneous rocks depend on?
4. Can you give an example of intrusive or plutonic rocks?
5. Are diorites intrusive or extrusive formations?
6. What do you know about batholiths?
7. Do pegmatites belong to the group of plutonic or volcanic rocks?
8. How do pegmatites occur?
9. What minerals are igneous rocks rich in?
3. ) :
1. adjacent layers )
2. abyssal rocks )
3. dimensions of crystals )
4. valuable minerals ) ()
5. shape and size of grains ) ()
6. mode of occurrence e)
7. coarse-grained )
8. uplifts )
9. zones of major deformation )
) :
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1. a) irregular shape
2. ) at a certain depth
3. ) economically important
4. ) solidified masses
5. ) scientific value
6. e) to cool slowly
7. ) existing types of rocks
8. ) fine-grained
9. ) fragmentary rocks
10. ) numerous cracks or fissures
10
band - n ; ; (); syn layer
cleave - v ; , ; cleavage n
constituent - n ,
define - v ,
distribute - v (among) (); ;
disturb - v ;
excess - n , ; ant deficiency
flaky - ;
fluid - n ;
foliate - v ; foliated - , ; syn flaky
marble - n
mention - v , ; n
plate - n ; ()
pressure - n ; rock pressure (underground pressure) ,
relate - v ; ; related ; relation - n ; relationship - n ; ; relative - ;
run (ran, run) - v , ; ; ( ); , ; (); (, )
schistose - a ;
sheet - n
slate - n ; syn shale
split (split) - v , , ; syn cleave
trace - n ; tracing n
at least
to give an opportunity (of) (-., -.)
in such a way
Metamorphic Rocks
The problem discussed concerns metamorphic rocks which compose the third large family of rocks. "Metamorphic" means "changed from". 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 undergo changes in texture, in mineral composition and structure and are transformed into metamorphic rocks. The process described is called metamorphism.
As is known, metamorphic rocks have been developed from earlier igneous and sedimentary rocks by the action of heat and pressure.
Gneisses, mica schists, phyllites, marbles, slate, quartz, etc. belong to the same group of rocks. Having the same mineral composition as granite, gneisses consist chiefly of quartz, orthoclase and mica. However unlike granite, they have a schistose structure. It means that their constituents are distributed in bands or layers and run parallel to each other in one direction. If disturbed the rock cleaves easily into separate plates.
The role of water in metamorphism is determined by at least four variable geologically related parameters: rock pressure, temperature, water pressure, and the amount of water present.
During a normal progressive metamorphism rock pressure and temperature are interdependent, and the amount of water and the pressure of water are related to the sediments and to the degree of metamorphism in such a way that, generally 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 consist 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 belong to the group of foliated metamorphic rocks. Marble and quartzite are non-foliated metamorphic rocks.
The structure of metamorphic rocks is of importance because it shows the nature of pre-existing rocks and the mechanism of metamorphic deformation. Every trace of original structure is of great importance to geologists. It gives an opportunity of analysing the causes of its metamorphism.
Being often called crystalline schists, metamorphic rocks such as 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.
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1. Generally speaking, metamorphic rocks have been developed from ores.
2. Marble, slate and phyllite belong to the group of metamorphic rocks.
3. As is known, unlike granite metamorphic rocks have a schistose 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 preexisting rocks and the mechanism of metamorphic deformation as well.
9. All metamorphic rocks are non-foliated.
2). :
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?
3. ) :
1. as a result of the chemical and physical changes
2. constituents of rocks
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
) pre-existing rocks
) 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
