Which type of rock may exhibit foliation due to pressure and heat?

• A. Sedimentary rock
• B. Extrusive rock
• C. Metamorphic rock
• D. Igneous rock

Answer: (C)

Foliation is a textural feature that develops in certain types of rocks under conditions of high pressure and temperature, typically in metamorphic rocks. Metamorphic rocks are formed from the alteration of existing rock types—igneous, sedimentary, or even other metamorphic rocks—through processes such as recrystallization, folding, and shearing.

In particular, foliation occurs as minerals realign under directional pressure, often resulting in a banded or layered appearance. Common examples of foliated metamorphic rocks include schist, slate, and gneiss. This distinctive characteristic is not exhibited in sedimentary rocks, as they primarily form through processes like compaction and cementation of sediments. Extrusive rocks, which are igneous rocks formed from lava that cools quickly at the Earth's surface, do not experience the conditions necessary for foliation either. Lastly, while some igneous rocks can show layering or banding, the processes that create foliation are linked specifically to the metamorphic transformation of rocks. Therefore, the correct answer regarding the type of rock that may exhibit foliation due to pressure and heat is indeed metamorphic rock.