Large-size crystals are known as phaneritic _.
The correct answer and explanation is:
Correct Answer: Phaneritic texture
Explanation (Approx. 300 words):
In geology, phaneritic texture refers to an igneous rock texture characterized by large, easily visible crystals that can be seen with the naked eye. The term “phaneritic” comes from the Greek word phaneros, meaning visible. This texture forms when magma cools slowly beneath the Earth’s surface, allowing the individual mineral crystals enough time to grow large.
Phaneritic textures are typically associated with intrusive (or plutonic) igneous rocks, which form underground. Common examples of rocks with phaneritic textures include granite, diorite, and gabbro. The slow cooling process within the Earth’s crust gives minerals the opportunity to develop into coarse grains that interlock, creating a visibly crystalline structure.
This contrasts with aphanitic textures, which form when lava cools rapidly on the Earth’s surface. Aphanitic rocks, such as basalt or rhyolite, have crystals too small to be seen without a microscope. The cooling rate is the primary factor determining whether an igneous rock will be phaneritic or aphanitic.
Phaneritic texture is significant because it provides clues about the formation history and environment of the rock. For example, the presence of a phaneritic texture in a granite sample indicates that it likely formed deep within a continental crust, where cooling took place over thousands to millions of years.
In summary, phaneritic texture refers to a rock with large, visible crystals, indicating slow cooling deep beneath the Earth’s surface. This term is not just a description but also a vital clue for geologists studying Earth’s internal processes and the history of igneous rock formation.