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UNIT 15
IGNEOUS ROCKS
Part 2

Task 1. Read and memorize the following words:
grain – дрібна частина, крихта; arrangement - упорядкування;
напрямок тріщин або жили розташування в певному порядку,
розміщення, розстановка,
класифікація, систематизація
aid - допомога quench - гасити
make inferences – зробити висновки porphyritic - порфіритовий
reveal – виявляти, показувати embedded - включений, вкраплений (у
породу) ; залягаючий (серед пластів)
refer to - давати посилання, посилатися glassy - склоподібний; прозорий
relatively - відносно interlocking - зв'язані один з одним
texture – текстура, структура molten blob – розплавлена крапля

Task 2. Transcribe and translate the following words: texture, aphanitic,
phaneritic, porphyritic, pyroclastic, pegmatitic, nonferromagnesian.

Task 3. Read the following text, translate it into Ukrainian.

Igneous Textures: What Can They Tell Us?
The term texture is used to describe the overall appearance of a rock based on the
size, shape, and arrangement of its mineral grains. Texture is an important property
because it reveals a great deal about the environment in which the rock formed. This
fact allows geologists to make inferences about a rock’s origin based on careful
observations of grain size and other characteristics of the rock.
Three factors influence the textures of igneous rocks: (1) the rate at which molten
rock cools; (2) the amount of silica present; and (3) the amount of dissolved gases in the
magma. Among these, the rate of cooling tends to be the dominant factor. Very large
magma body located many kilometers beneath Earth’s surface will cool over a period of
perhaps tens to hundreds of thousands of years.

Types of Igneous Textures
Aphanitic (fine-grained) texture. Igneous rocks that form at the surface, or as
small intrusive masses within the upper crust where cooling is relatively rapid, exhibit a
fine-grained intrusive texture, also termed an aphanitic texture. The crystals that make
up aphanitic rocks are so small that individual minerals can only be distinguished with
the aid of a polarizing microscope or other sophisticated techniques. Therefore, we
commonly characterize fine-grained rocks as being light, intermediate, or dark in color.
Using this system of grouping, light-colored aphanitic rocks are those containing
primarily light-colored nonferromagnesian silicate minerals.
Phaneritic (coarse-grained) texture. When large masses of magma slowly
crystallize at great depth, they form igneous rocks that exhibit a coarse-grained texture
also referred to as a phaneritic texture. Coarse-grained rocks consist of a mass of
intergrown crystals that are roughly equal in size and large enough so that the individual
minerals can be identified without the aid of a microscope.
Porphyritic texture. A large mass of magma may require tens to hundreds of
thousands of years to solidify. Because different minerals crystallize under different
environmental conditions (temperatures and pressure), it is possible for crystals of one
mineral to become quite large before others even begin to form. Should molten rock

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