What distinguishes metamorphic rocks from igneous rocks?

Metamorphic rocks are distinguished from igneous rocks primarily by their formation process and texture. Metamorphic rocks are created through the alteration of existing rocks—in most cases, either igneous, sedimentary, or even other metamorphic rocks—under high pressure and temperature conditions, which leads to changes in mineral composition and structure.

The correct answer indicates that metamorphic rocks often exhibit a texture characterized by visible crystals that form as minerals recrystallize during the metamorphic process. This recrystallization often results in a foliation or banding effect, giving metamorphic rocks a unique appearance that can include visible, larger crystals that were not present in the original rock.

In contrast, the other choices highlight characteristics usually associated with different types of rocks or processes. For example, the presence of fossils is typical of sedimentary rocks, not metamorphic or igneous. Rocks that form from sediment are directly classified as sedimentary rocks, rather than metamorphic. Erosion is a process that contributes to sedimentary rock formation, not metamorphic rock. Thus, the unique characteristics of crystal formation in metamorphic rocks set them apart from aforementioned types.