39. Закончите предложения подходящими по смыслу слотами из текста б:

1. As for the origin of metamorphic rocks they ....

2. When we say that a mineral has a schistose structure it means ... .

3. It should be noted that the role of water in the formation of metamorphic rocks is great. It is known that high-grade metamorphic rocks are characterized by the absence of water while medium-grade rocks... .

4. Geologists should know every trace of the original structure of metamorphic rocks because ....

40. Суммируйте содержание текста б, используя слова в скобках:

1. The process of metamorphism. (to mean, to show, to undergo changes, to be transformed, to call)

2. The role of water in the formation of metamorphic rocks, (to be interdependent, to be related to, in such a way, generally speaking, to be characterized by)

134 UnitS

3. The difference between foliated and non-foliated metamor­ phic rocks, (flaky, to cause, to split into, to cleave)

4. The structure of metamorphic rocks, (to be of importance, trace, pre-existing rocks, to give an opportunity of)

41. Расскажите коротко (8-10 предложений), что вы знаете о горных поро­дах в земной коре, об их происхождении, залегания н минералах, которыми они богаты. Используйте данную ниже схему н следующие разговорные формулы:

as for as I know; as is known; as for; I'd like to say a few words about...; it should be noted that...; as a rule; generally speaking и др.

Rocks of the Earth's Crust

I I

sedimentary rocks igneous rocks metamorphic rocks

I I I

mechanical, chemical intrusive rocks, rocks structure

and organic extrusive (volcano) |

sediments rocks water in metamorphism

I I I

Practical value of each type of rocks (metals they are rich in)

42. Прочитайте текст в без словаря и скажите, о чем ои. Слова для понимания текста:

profit — прибыль; польза

residual — осадочный

alloy — сплав

cast iron — чугун

ТЕКСТ В

Minerals that make up rocks, are defined as inorganic sub­stances which occur naturally and have a definite chemical composi­tion and physical properties which vary within known limits.

The major properties are colour, crystal form, hardness, cleavage and others. Cleavage is one of the most diagnostically useful mineralogi-cal properties which can be found throughout the mineral.

Minerals of use to man can be grouped into two broad catego­ries: 1) metals, such as aluminium, copper, gold, silver, iron, tin, platinum, chromium, nickel, lead and zinc, and 2) non-me­tallic minerals, such as diamonds, salt, limestone, cement, sul­phur, and asbestos. When minerals occur so that they can be worked at a profit they are called ore deposits. Mineral deposits are seldom equally rich throughout.

Unit 5 135

Economic minerals are those which are of economic impor­tance and include both metallic and non-metallic minerals.

Most minerals consist of several elements. Such elements are oxygen, silicon, titanium, aluminium, iron, magnesium, calcium, sodium, potassium and hydrogen. They make up more than 99 per cent by weight of all the rock-forming minerals. Of these, alu­minium, iron and magnesium are industrial metals. The other metals are present in small quantities, mostly in igneous rocks.

For example, iron is one of the most abundant metals in the Earth's crust. There are three important classes of iron deposits: deposits associated with igneous rocks; residual deposits and sedi­mentary deposits. Iron deposits associated with igneous rocks are usually small but very rich bodies either of haematite or magnetite. Large concentrations have been successfully mined in Pennsylvania (the USA) and in the Russian Federation.

Residual deposits of iron minerals are formed wherever weather­ing occurs. Iron deposits formed this way are very widespread. It should be stressed that the residual deposits were among the first to be exploited by man.

Sedimentary iron deposits make up most of the world's current production.

As the essential component of every variety of steel, iron is ob­viously the most important of all industrial metals. It has played a large part in the development of our modern civilization. Iron ores are mainly used for producing cast iron, steels and ferro-alloys. From a scientific point of view, iron's most important property is that it becomes magnetized.

The magnetic iron ore is the main wealth of the Kursk Magnetic Anomaly (KMA). It is necessary to say that only in the last century was the secret of the unusual magnetism of enormous iron ore masses discovered underground.

Iron fields are worked by surface mining which is more eco­nomical. But the KMA is rich not only in iron ores. Its deposits contain bauxite, phosphorite, cement, sand and clays.