Apr 21 2014
Igneous textures are used by geologists in identifying the origin of rocks, and for the classification of rocks. Phaneritic texture is one of the six main textures of rocks. Phaneritic rocks are intrusive igneous rocks with coarse crystals of equal size.
Phaneritic rocks indicate slow cooling of magma deep beneath the Earth’s surface. With slow cooling, the rate of growth of mineral grains exceeds the rate of nuclei formation within the minerals of the rocks. As a result, relatively large mineral grains are formed, yielding a phaneritic texture.
The minerals in the phaneritic igneous rock are large, and can be observed as individual crystals with the naked eye. The diameter of each crystal may range from 1 to 30mm. The crystals that are formed during early stages of slow cooling are euhedral, while the later formed crystals are subhedral to anhedral.
Phaneritic textures are subdivided into coarse, medium, and fine-grained. Coarse-grained textures are generally associated with larger or deeper intrusions. Fine-grained textures are formed in shallow, plutonic structures, such as sills and dikes. Examples of phaneritic igneous rock include diorite, gabbro, and granite.
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