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11. Read the text and translate it into Russian.
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11. Read the text and translate it into Russian.
Minerals
Minerals are the basic naturally occurring inorganic homogeneous units having definite physical and chemical properties, which are combined in various ways and under different conditions to form rocks.
Most minerals consist of elements combined as chemical compounds although a few may occur as native elements, – for example, gold, silver, copper, and carbon (diamond and graphite).
Minerals form under many different conditions, but for each mineral there is a specific range of temperature, pressure, and other conditions under which it is stable.
Minerals are stable only in the environment in which they are formed. For example, olivine forms at depth; it commonly crystallizes from magma under relatively high temperatures and pressures. If olivine is exposed to the temperature, pressure, and humidity of the earth’s surface, it is no longer stable and the crystal structure disintegrates.
If clay minerals, which formed at the surface of the earth, are deeply buried or subjected to heat and pressure, they change to micas, which are stable under new conditions.
A few minerals, such as quartz, are stable under a range of conditions. However, most minerals are not, and since conditions at specific places on the earth’s surface commonly change, minerals change too. Because of crustal movements, minerals, which formed at the surface, are commonly subjected to the conditions at depth, and minerals, which formed at depth, are commonly exposed at the surface.
Consequently, change, not stability is the rule.
Feldspars. The feldspars are probably more widely distributed than any other group of rock-forming minerals. They occur in most of the igneous rocks, such as granites and lavas; in certain sandstones and conglomerates among sedimentary ones; and in gneisses of the metamorphic rocks.
Feldspar is a family name and not that of a single mineral. It constitutes one of the most, if not the most, important group of rock-forming minerals; nearly 60% of the earth’s crust is composed of feldspars.
It possesses good cleavage in two directions. Brittle. Specific gravity varies with chemical composition. Lustre is vitreous, on the cleavage faces often pearly. Streak is white, not characteristic. The feldspar exhibits a variety of colours: colourless, sometimes transparent and glassy, white, grey, red, and green. Feldspar is frequently the dominant colouring mineral in granites.
Quartz. Quartz is the second most abundant mineral in the Earth’s crust, after feldspar. It consists of silica – a compound of silicon and oxygen. It forms the major proportion of most sands.
Quartz is crystalline, possesses no cleavage, colour varies widely from colourless or white through grey and brown to black. Lustre is vitreous, sometimes greasy. Streak is white. It is brittle.
Quartz has widespread occurrence in igneous, sedimentary and metamorphic rocks. It is an important constituent of the acid igneous rocks, such as granites, may occur in gneisses, and is the predominant constituent in quartzite. It is common in sedimentary rocks, forming the principal minerals in sandstones. It is associated in rocks chiefly with feldspar.
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(from: L. Dolinskaya, N. Kitkova, T. Safyannikova. Express English for Geo-students)
12. Find in the text and read out English equivalents of these words and word-combinations.
Иметь физические свойства, иметь химические свойства, соединяться различным образом, при различных условиях, образовывать горные породы, минералы состоят из, химические соединения, самородный элемент, серебро, медь, углерод, алмаз, графит, изумруд, рубин, гранат, земная кора, наиболее распространенный элемент, образовывать минералы, образовывать оксиды, встречаться в природе, подвергаться высокой температуре, подвергаться влажности, кристаллическая структура разрушается, оказаться глубоко под землей, образоваться на поверхности земли, образоваться на глубине, превратиться в слюду, обладать совершенной спайностью, хрупкий минерал, поверхности спайности, иметь широкое распространение, важный компонент, высокая отражательная способность, драгоценный камень, кристаллизуется из магмы.
13. Answer the following questions.
1. What is a mineral?
2. Do all minerals occur as chemical compounds? What minerals may occur as native elements?
3. Are minerals stable under different conditions?
4. What is feldspar? What properties does it possess?
5. What chemical elements does quartz consist of? What properties does quartz possess?
14. Agree or disagree with the statements below:
1. A mineral is a naturally occurring inorganic substance that is solid and stable at room temperature, representable by a chemical formula, and has an ordered atomic structure.
2. Minerals result from the activity of living organisms.
3. Minerals occur only as native elements.
4. Gold is a chemical compound.
5. A mineral is a naturally occurring liquid inorganic substance.
6. The study of minerals is called hydrogeology.
7. Feldspars can be found in igneous, metamorphic and sedimentary rocks.
8. Feldspar is the second most abundant mineral in the Earth’s crust. It is made of silicon and oxygen combined together as SiO2.
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