Read the following text and fulfill the after reading exercises.
Some sedimentary rocks and minerals consist of chemicals that had been once dissolved in water.
Certain limestones formed this way. Oolitic limestone consists of billions of oolites: tiny balls produced by calcium carbonate accumulating on particles rolled around by gentle currents in warm, shallow seas. Oolite forms like this today on the Bahama Banks. Dolomitic limestone (limestone mainly made of the mineral dolomite) occurs where certain brines chemically alter preexisting limestone or where dolomite deposits form in an evaporating sea. Such so-called evaporites underlie one-quarter of the continents in beds up to 4,000 ft (1220 m) thick. Evaporites form now where chemical deposits accumulate in evaporating desert takes and coastal salt flats. But certain old evaporites could have been precipitated from chemically oversaturated deep offshore waters of almost landlocked seas such as the Mediterranean.
Three main minerals tend to settle in a sequence. First comes calcium carbonate. Next is gypsum (a granular crystalline form of calcium sulfate combined with water. Then comes sodium chloride in the form of halite (rock salt.) This is a soft, low density rock and liable to flow. Pressure from overlying rock forces up huge plugs / domes of salt beneath the coast of Texas and Louisiana and in parts of Germany, Iran and Russia.
Besides the rocks and minerals just named, there are other chemical deposits. A few have or had important economic uses – particularly borax, chert and flint; certain iron-rich compounds, nitrates and phosphorites. But some of these are partly biological in origin; and scientists disagree about how certain forms of iron occurred.
(David Lambert “The Field Guide to Geology” 1988, Cambridge University Press)
Fig. 31 Rock salt
Fig. 32 A combination of gypsum (light colored) and anhydrite (darker bands)
Match the words with the Russian equivalent.
1. to consist of а. перевисать; выдавливать
2. to dissolve in b. подверженный чему-либо
3. to produce c. соединять; сочетать
4. to accumulate d. осаждать; оседать
5. to roll around e. лежать в основе
6. to be made of f. выпадать в осадок
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7. to alter g. изменять(ся)
8. to form h. образовывать; составлять
9. to underlie i. переворачивать(ся)
10.to precipitate j. созданный; изготовленный
11.to settle k. создавать; порождать
12.to combine with l. накапливать(ся)
13.to be liable to m. состояться; заключаться
14.to force up n. растворяться
Translate the following word combinations and phrases.
1. rocks and minerals consist of chemicals
2. tiny balls are produced by calcium carbonate accumulating on particles
3. limestone is mainly made of the mineral dolomite
4. limestone occurs where certain brines chemically alter preexisting rocks
5. evaporites underlie one-quarter of the continent
6. chemical deposits accumulate in evaporating desert lakes
7. three main minerals settle in a sequence
8. soft, low density rock are liable to flow
9. pressure forces up huge plugs
10.certain old evaporites precipitate from chemically oversaturated deep offshore waters
Compose questions to the text, using the following Wh-words: what, which, where, when, how
EX. Oolitic limestone consists of billions of oolitites. WHAT does oolitic limestone consist of?
3.2 INFORMATIVE READING- Rocks from fragments 3.2.1 Read the text (Part 1, Part 2) and for statements 1-12, choose the best answer: A, B, C or D. Then explain the words in bold.
Part 1
Most sedimentary rocks form from particles eroded from the rocks on land. Their main ingredients are clasts (rock fragments) of quartz, feldspar and clay minerals. These fragments range in size from microscopic grains to boulders. More than 90% of all sedimentary rock contains particles no bigger than a sand grain. Many geologists classify such particles by size in two main groups. The (fine-grained) lutites with grains less than 0.06 mm diameter produce mudstone, siltstone and shale. The (medium-grained) arenites or sandstones with grains of 0.06-2 mm give arkose, graywacke and orthoquartzite. Here are brief descriptions of six fine- and medium- grained rocks.
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1. Mudstone- solid rock made of clay minerals of less than 0.004mm diameter.
2. Shale - mudstone, siltstone or similar fine-grained rock of silt and clay split easily along its bedding planes. Shale accounts for more than 80% of all sedimentary rock.
3. Siltstone- rock formed of particles 0.004-0.06mm in diameter.
4. Orthoquartzite - a “clean” or pure arenite mainly made of quartz after other substances have been removed. (Arenites account for more than 10% of all sedimentary rock)
5. Arkose - an arenite rich in feldspar derived from gneiss or granite.
6. Graywacke - a muddy, often grayish sandstone with mixed-size particles including quartz, clay minerals and others.
Fig.33 Ferruginous sandstone
Part 2
Rudites (from the Latin rudis - coarse) are clasts (rock fragments) coarser than a sand grain. Mixes with finer particles, rudites can be consolidated into natural concretes called conglomerates and breccias.
Conglomerates are named from the Latin for “lumped together”. They contain rounded fragments – pebbles, cobbles and boulders – and often represent waterborne and watersorted remnants of eroded mountain ranges or retreating rocky coasts. They accumulate along mountain fronts, in shallow coastal waters, and elsewhere; becoming mixed with sand, then bound by natural cement. How clasts in a conglomerate lie sorted, packed and graded offers clues to how or where it was laid down. The thickest masses of conglomerate – as in the Siwalik Formation of the Himalayas’ foothills – mark the aftermath of an orogeny.
Breccias (from the Italian for “rubble”) are rocks containing sharp-edged, unworn, usually poorly sorted fragments, often embedded in a clay-rich matrix. Breccias form usually near their place of origin; their clasts have not been carried far enough to suffer rounding by abrasion. Many breccias originate in talus, deserts, mudslides, faulting, meteorite impact, or shrinkage of evaporite beds.
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Authorities tend to separate conglomerates and breccias from tillites – poorly sorted, ice-eroded, ice-borne debris consolidated into solid rock. Many tillite clasts are faceted, with slightly rounded edges. Ancient tillites occur in South America, Africa, India and Australia.
(David Lambert “The Field Guide to Geology” 1988, Cambridge University Press)
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Fig. 34 Conglomerate
1. Most sedimentary rocks are formed from
A. eroded rocks
B. eroded particles
C. eroded sand
2. The size of particles in sedimentary rocks
A. bigger than sand grain
B. no bigger than sand grain
C. the same as sand grain
3. Geologists divide particles by size into
A. two groups
B. three groups
C. four groups
4. Lutites are
A. medium-grained
B. coarse-grained
C. fine-grained
5. An example of arenites are
A. sandstones
B. greywacke
C. siltstone
6. Fine-grained rocks are
A. mudstone, shale, orthoquartzite
B. mudstone, shale, siltstone
C. shale, arkose, graywacke
Fig. 35 Breccia
7. Rudites can be consolidated into natural concretes called
A. conglomerates and breccias
B. clasts and conglomerates
C. breccias and clasts
8. Conglomerates is a Latin word which means
A. coarse
B. rubble
C. lumped together
9. Conglomerates accumulate in
A. shallow coastal waters
B. shallow lakes
C. shallow coast lines
10. Conglomerates contain
A. rounded fragments
B. coarse debris
C. poorly sorted fragments
11. Breccias is usually embodies in
A. natural cement-sand
B. solid rock
C. clay-rich matrix
12. Tillites are different from conglomerates and breccias because
A. clasts with slightly rounded edges
B. ice-eroded debris
C. poorly sorted fragments
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