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Geol Igneous Rocks

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Geology
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Among the six rocks, rocks A and C are the light-colored (almost beige) ones. Hence, their classification as
light (Felsic). Rocks B and D are greyish rocks and thus fall in the category of intermediate rocks. Rocks E
and F are dark-colored, indicating they are rich in ferro-magnesian minerals. These rocks are classified as
dark (mafic)-colored igneous rocks.
The texture of the rock samples is classified based on the size of crystals. If you will look at rocks A and F,
their crystals are not noticeable by the naked eye. These rocks are therefore classified as aphanitic.
Aphanitic rocks are also classified as volcanic rocks because they are rapidly cooled and formed above or
near the surface of the Earth resulting in small crystal size. In contrast, crystals are highly noticeable in
rocks B and E, these rocks are said to be phaneritic and plutonic in nature. The large crystals in these
rocks are a result of slow cooling below the Earth. Of course, there are rock samples which contain large
and small crystals such as in rocks C and D. Rocks which have a mixture of texture are classified as
porphyritic. Rock C is classified as phaneritic-porphyritic because its large crystals (hence, phaneritic and
plutonic) are mixed with larger, darker crystals (hence porphyritic). Rock D is a combination of fine crystals
and dark, slender crystals and classified as aphanitic-porphyritic and volcanic.
Aphanitic (felsic rocks) are named rhyolite (Rock A). These rocks are volcanic rocks found near the
continent-continent collision zones. Phaneritic felsic rocks are called granite. They are plutonic and found
deep in the continent-continent collision zones.
Mafic rocks are found in the mid-ocean ridges. When these mafic rocks have a phaneritic texture and
formed below the earth, they are called gabbro. If they have a phaneritic texture and are formed near the
surface of the earth, they are named basalt.
In near-surface subduction zones, rocks with aphanitic texture are formed. These rocks are called andesite.
Beneath the earth, diorite rocks with phaneritic texture are formed.

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Among the six rocks, rocks A and C are the light-colored (almost beige) ones. Hence, their classification as light (Felsic). Rocks B and D are greyish rocks and thus fall in the category of intermediate rocks. Rocks E and F are dark-colored, indicating they are rich in ferro-magnesian minerals. Thes ...
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