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Task 2. Read the text. Translate it into Ukrainian.

Felsic (Granitic) Igneous Rocks
GRANITE. Granite is perhaps the best known of all igneous rocks. This is
partly because of its natural beauty, which is enhanced when it is polished, and partly
because of its abundance in the continental crust. Slabs of polished granite are
commonly used for tombstones and monuments and as building stones. Granite is a
coarse-grained rock composed of about 25 % quartz and roughly 65 percent feldspar,
mostly potassium-and sodium-rich varieties. Other minor constituents of granite include
muscovite and some dark silicates, particularly biotite and amphibole. When potassium
feldspar is dominant and dark pink in color, granite appears reddish. However, the
feldspar grains are more often white to gray, so when they are mixed with lesser
amounts of dark silicates, granite appears light gray in color.
RHYOLITE. Rhyolite is the extrusive equivalent of granite and, like granite, is
composed essentially of the light-colored silicates. This fact accounts for its color,
which is usually buff to pink or occasionally very light gray. Rhyolite is fine-grained
and frequently contains glass fragments and voids, indicating rapid cooling in a surface
environment. In contrast to granite, which is widely distributed as large plutonic masses,
rhyolite deposits are less common and generally less voluminous.
OBSIDIAN. Obsidian is a dark-colored glassy rock that usually forms when
silica-rich lava is quenched quickly. In contrast to the orderly arrangement of ions
characteristic of minerals, the ions in glass are unordered. Consequently, glassy rocks
such as obsidian are not composed of minerals in the same sense as most other rocks.
PUMICE. Pumice is a volcanic rock with a glassy texture that forms when large
amounts of gas escape through silica-rich lava to generate a gray, frothy mass. In some
samples, the voids are quite noticeable, whereas in others the pumice resembles fine
shards of intertwined glass. Because of the large percentage of voids, many samples of
pumice will float when placed in water.
Intermediate (Andesitic) Igneous Rocks
ANDESITE. Andesite is a medium-gray, fine-grained rock of volcanic origin.
Its name comes from South America’s Andes Mountains, where numerous volcanoes
are composed of this rock type. Andesite commonly exhibits a porphyritic texture.
Andesite often resembles rhyolite, so their identification usually requires microscopic
examination to verify mineral make-up.
DIORITE. Diorite is the plutonic equivalent of andesite. It is a phaneritic rock
that looks somewhat similar to gray granite. However, it can be distinguished from
granite by the absence of visible quartz crystals and because it contains a higher
percentage of dark silicate minerals. Diorite has a salt-and-pepper appearance.

Task 3. Look at Figure 15.2 and Figure 15.3. They provide the classification
of major igneous rocks based on mineral composition and texture. Adding the
information from the figures try to characterize:
 granite;
 rhyolite;
 obsidian;
 pumice;
 andesite;
 diorite.

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