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Read the following text and fulfill after-reading tasks.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 large 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, uplifted 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 batholiths 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 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 thickness 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 flow 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 lava types. It is the principal rock type of the ocean floor. (М.Я. Баракова, Р. И. Журавлева, Английский язык для горных инженеров, М. 2001)
Fig. 27. Various modes of occurrence of igneous rocks
Read the following phrases and give the Russian equivalent.
Can these terms and phrases be understood without translating? Why? Intrusiveand extrusiverocks; plutonic intrusion; large crystals; volcanic rocks; mountain zones; zones of major deformation; mineral grains; granitesanddiorites; the group of intrusiveor plutonicrocks; straight parallelwalls; gigantic crystals; slowly-cooled batholiths; thick laccoliths; otherplutonites; coarse-grainedpegmatites; lava flow.
State, which sentences, is T (true) or F (false) 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 as intrusive rocks. 4. The grain size of igneous rocks depends on mode o 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.
Match the English terms with the Russian equivalents.
Match the Russian terms with the English equivalents.
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