Which of the following rocks is an example of metamorphic rock?

Gneiss is considered a metamorphic rock because it is formed through the process of metamorphism, which involves the transformation of existing rock types (in this case, igneous or sedimentary rocks) under conditions of high pressure and temperature. During metamorphism, the original minerals in the rock can recrystallize or change in alignment, leading to the banded texture characteristic of gneiss.

Metamorphic rocks like gneiss are typically found in regions that have undergone significant geological processes, such as mountain-building events, where intense pressure and heat alter the minerals within the original rock. This is what differentiates it from other rock types such as shale, limestone, and granite, which are classified as sedimentary and igneous rocks, respectively, and form under different conditions.

The recognition of gneiss as a metamorphic rock highlights the dynamic nature of Earth's crust and allows for greater understanding of geological processes over geological time scales.