Which type of rock forms from the alteration of existing rocks due to heat and pressure?

Metamorphic rocks form from the alteration of existing rocks through the application of heat and pressure over long periods. This process can transform sedimentary rocks, igneous rocks, or even other metamorphic rocks into new types, often resulting in significant changes in mineral composition and texture. The extreme conditions cause the minerals within the rock to crystallize and realign, leading to the formation of features such as foliation or banding.

Sedimentary rocks form from the accumulation of sediments, while igneous rocks result from the cooling and solidification of magma or lava. Volcanic rocks are a subset of igneous rocks that specifically originate from volcanic eruptions. None of these processes involve the alteration due to heat and pressure characteristic of metamorphic rocks, highlighting why the correct choice is metamorphic.