Text 3 Rocks (6400)

1. Learn the words and word combinations before reading:

connote - [kO'nqut] - обозначать, подразумевать

specimen - ['spesimin] - образец, экземпляр

exposure - [iks'pquZq] - подвергание воздействию, обнажение (горных пород)

igneous - ['igniqs] - изверженный

crystallization - ["kristqlai'zeiSqn] - кристаллизация

abyssal - [q'bisql] - глубинный, изверженный, абиссальный

adjacent geological stratum - [q'dZeisqnt] - смежный геологический слой

host - [hqust] - принимать, притягивать

tungsten - ['tANstqn]   - вольфрам

uranium - [ju'reinjqm] - уран

granite - ['grxnit] - гранит

chromium - ['krqumjqm]   - хром

occurrence - [q'kArqns] - залегание, месторождение

texture - ['tekstSq] - строение, структура минералов, почвы, поверхности

geometry - [dZi'Omitri] - геометрия

distortion - [dis'tLSqn] - кручение, перекручивание

facies - внешний вид, общий облик, фация

index mineral – руководящий материал

gneiss - [nais] - гнейс, порода, состоящая из шпата, кварца и слюды

valuable - ['vxljuqbl] - ценный, полезный

sillimanite - силлиманит

kyanite ['kiq"nit] -кианит, дистен

staurolite ['storq"lit] – ставролит

olivines - оливин, хризолит, перидот

pyroxenes - ['pairOksJn] - пироксен

amphiboles - ['amfq"bol] – обманка (любая группа минералов с комплексом силикатных материалов, содержащих кальций, натрий, магний, алюминий и ионы железа или их соединение)

mica - ['maikq]   - слюда

feldspar - ['feldspa:] - полевой шпат

2. Read and translate the text:

Broadly speaking a rock is an assemblage of one or (most commonly) two or more minerals (specific chemical compounds) that form a part of the Earth’s solid body. A “rock” normally connotes an individual “specimen” – one that can be held in one’s hand or is larger but detached from its outcrop (exposure of the rock’s source) so that it has visible boundaries. We know all rocks to fall into three great divisions termed: 1) sedimentary, 2) igneous, 3) metamorphic. In this text we’ll read about two of them: igneous and metamorphic.

Igneous rocks (from Latin “ignis”, fire) are one of the three main rock types. Igneous rocks are formed by solidification of cooled magma (molten rock).

Igneous rocks that have solidified without reaching the surface are termed intrusive or abyssal. Those which have flown out on the surface as lava before solidifying are termed effusive or volcanic.

Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth’s crust. These have diverse properties, depending on their composition and how they were formed. Igneous rocks make up approximately ninety-five percent of the upper part of the Earth’s crust, but their great abundance is hidden on the Earth’s surface by a relatively thin but widespread layer of sedimentary and metamorphic rocks.

Igneous rocks are geologically important because:

• their minerals and global chemistry give information about the composition of the mantle, from which some igneous rocks are extracted, and the temperature and pressure conditions that allowed this extraction, and of other pre-existing rocks that melted;

• their absolute ages can be obtained from various forms of radiometric dating and thus can be compared to adjacent geological strata, allowing a time sequence of events;

• their features are usually characteristic of a specific tectonic environment, allowing tectonic reconstitutions;

• in some special circumstances they host important mineral deposits (ores): for example, tungsten, tin, and uranium are commonly associated with granites, whereas ores of chromium and platinum are commonly associated with gabbros.

Typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes.

Igneous rocks are classified according to mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body.

Metamorphic rocks are the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means “change in form”. The protolith is subjected to heat and pressure (temperatures greater than 150 to 200 °C and pressures of 1500 bars) causing profound physical and chemical change. Metamorphic rocks make up a large part of the Earth’s crust and are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath the Earth’s surface, subjected to high temperatures and the great pressure of the rock layers above. They can be formed by tectonic processes such as continental collisions which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth’s interior. The study of metamorphic rocks (now exposed at the Earth’s surface following erosion and uplift) provides us with very valuable information about the temperatures and pressures that occur at great depths within the Earth’s crust. Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite.

Metamorphic minerals are those that form only at the high temperatures and pressures associated with the process of metamorphism. These minerals include sillimanite, kyanite, staurolite, andalusite, and some garnet.Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz, may be found in metamorphic rocks, but are not necessarily the result of the process of metamorphism. These minerals formed during the crystallization of igneous rocks. They are stable at high temperatures and pressures and may remain chemically unchanged during the metamorphic process. However, all minerals are stable only within certain limits, and the presence of some minerals in metamorphic rocks indicates the approximate temperatures and pressures at which they were formed.

3. Determine the form of the underlined tense structures.

4. Find the gerunds in the text.

5. After reading the text answer the following questions:

1. What is a rock? 2. What are the main rock types? 3. What does the word “igneous” mean? 4. How many per cent of the upper part of the Earth’s crust do the igneous rocks make up? 5. Why are igneous rocks so geologicaly important? 6. What does the word “metamorphism” mean? 7. What does the study of metamorphic rocks provide us with? 8. What metamorphic minerals can you name?