Final answer:
Phaneritic igneous rocks are characterized by having crystals large enough to see, which form due to slow cooling of magma deep within the Earth. These rocks can range from mafic to felsic in composition based on the minerals present, but their defining feature is the crystal size, not mineral content alone.
Step-by-step explanation:
Phaneritic igneous rocks are identified by the texture of the minerals they contain. The key feature of phaneritic rocks is that they have crystals large enough to be seen without magnification.
This texture arises from the slow cooling of magma deep within the Earth, which allows the crystals to grow to a recognizable size.
These rocks are also known as intrusive or plutonic rocks. The mineral composition of phaneritic rocks can include a range of minerals from mafic to felsic, but their classification does not solely depend on the minerals present.
Instead, it is the size of the crystals that is the hallmark of phaneritic textures.
The mineralogy of an igneous rock gives clues about its classification. For example, a rock with a considerable amount of light-colored minerals like quartz or feldspar is referred to as felsic, whereas one with more dark-colored, magnesium, or iron-rich minerals such as olivine or pyroxene is considered mafic.
It is important to note that phaneritic rocks can exhibit a variety of mineral compositions, and their identifying feature remains the visibly large crystals.