Ex. 3. Read text a and name the characteristic features of Igneous Rocks. Text a

Igneous Rocks

Igneous rocks have crystallized from solidified magma.

Igneous rocks can be classified in a number of ways and one of them 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 bathliths 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.

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 their sizes 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.lt is the principal rock type of the ocean 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.

Ex. 4. Which sentences are true according to the text?

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.

Ex. 5. Answer these questions.

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?

Ex. 6. Find in the right column Russian equivalents of these words.

1. adjacent layers а) способ залегания

2. abyssal rocks б) крупнозернистый

3. dimensions of crystals в) зоны крупных нарушений

4. valuable minerals г) абиссальные (глубинные) породы

5. shape and size of grains д) смежные пласты (слои)

6. mode of occurrence e) размеры кристаллов

7. coarse-grained ж) взбросы

8. uplifts з) форма и размер зерен

9. zones of major deformation и) ценные минералы

Ex. 7. Find in the right column English equivalents of these words.

1. затвердевшие массы a) irregular shape

2. обломочные породы b) at a certain depth

3. медленно остывать c) economically important

4. мелкозернистый d) solidified masses

5. многочисленные трещины e) scientific value

6. неправильная форма f) to cool slowly

7. на определенной глубине g) existing types of rocks

8. экономически важный h) fine-grained

9. научная ценность i) fragmentary rocks

10. существующие типы пород j) numerous cracks or fissures

Ex. 8. Translate these word combinations paying attention to participle.

accelerated process, weathered fragments of rocks, crystallized magma, generally applied method, successfully improved design, unconsolidated and consolidated rocks, weakly deformed minerals, unfrozen ground, rapidly cooled rocks, detailed studies of the Earth's crust, utilized equipment, dissolved minerals, minerals dissolved by the consolidated rocks, action of water, rocks consolidated by some substances, rocks formed by solidification, stratified sediments, rocks exposed on the Earth's surface, transformations caused by new conditions...

Ex. 9. Finish the sentences using suitable words from text A.

1. Batholiths are composed of... .

2. Laccoliths are very similar to sills but sills ... .

3. Granites belong to the group of... .

4. Pegmatites are also ....

5. Dykes are intrusive bodies which ... .

6. Extrusive rocks have been formed from ....

7. As for the origin of intrusive rocks, they ... ,

8. The grain size of igneous rocks may be different. For ex­ample ....

Ex. 10. Express your disagreement with the statements. Prove your opinion

with the facts from the text. Use these conversational formulas.

It seems to be wrong; I don't agree with yon; I don't think so; on the con­trary; that's not quite so; as far as I know

1. Igneous rocks have been formed by sedimentation. Nothing is written about different types of these rocks.

2. One cannot explain the fact that exposed igneous rocks are most numerous in mountain zones.

3. Granites and diorites belong to the group of extrusive rocks and their mode of occurrence is unknown.

4. Plutonic or abyssal rocks are extrusive rocks with grain size less than 0.5 mm.

Ex. 11. Summerize text A using these words and expressions:

The formation of igneous rocks and their types, (to be formed, to solidify, to cool, either ... or, magma, volcano, lava, fragmentary rocks)

The grain size of igneous rocks and its dependence on the mode of occurrence, (grain size, plutonic or abyssal rocks, extrusive and volcanic rocks)

The causes of exposed rocks formation in mountain zones. (various depths, zones of major deformation, uplifts, erosion)

Granites and diorites and their mode of occurrence, (intrusive rock, to occur as..., irregular mass, stocks, dykes, occurrences, at a certain depth)

Pegmatites and their mode of occurrence, (plutonic rocks, to occur, vein, to cut through, as well as adjacent rocks)

Ex. 12. Read these words and try to remember them.

band - слой; полоса; про­слоек (породы); syn layer cleave - расщепляться; трескаться, отделяться по кливажу cleavage - кливаж constituent - состав­ная часть, компонент define - определять, да­вать определение distribute (among) - рас­пределять (между); раздавать disturb - нарушать; смещать excess - избыток, изли­шек; ant deficiency flaky - слоистый; похожий на хлопья fluid - жидкость; жидкая или газообразная среда foliate - расщепляться на тонкие слои foliated - лис­товатый, тонкослоистый; syn flaky marble - мрамор mention - упоминать, ссылаться; упоминание

plate - пластина; полоса (металла) pressure - давление; rock pressure (underground pressure) горное давление, давление горных пород relate - относиться; иметь отношение; related - родствен­ный relation - отношение; re­lationship - родство; свойство; relative - относительный; соответственный run (ran, run) - бегать, двигаться; течь; работать (о машине); тянуться, прости­раться; управлять (машиной); вести (дело, предприятие) schistose - сланцеватый; слоистый sheet - полоса slate - сланец; syn shale split (split) - раскалываться, расщепляться, трескаться; syn cleave trace - след; tracing - про­слеживание

Ex. 13. Read the words and translate them.

cleavage distribution the definition of rocks

geological disturbances schistose structure

schistose coal low-grade metals

medium-grade coals high-grade oil

exposed igneous rocks the Earth's surface

separate plates single oithoclase crystals

chemically active fluids scientific value

rock pressure water pressure

excess of water thin sheets

foliated and non-foliated metamorphic rocks

the most common metamorphic rocks

Ex. 14. Read text B and find the answers to these questions:

What is metamorphism?

Why can metamorphic rocks cleave easily?

Why is the study of metamorphic rocks important?