Which type of rock is formed by extreme heat and pressure?

Metamorphic rock is formed under conditions of extreme heat and pressure, which typically occurs deep within the Earth's crust. This process transforms pre-existing rocks, which can be either igneous, sedimentary, or even other metamorphic rocks. The heat causes mineral recrystallization while the pressure can lead to foliation and changes in the texture and composition of the rock.

The formation of metamorphic rock is a key aspect of the rock cycle, illustrating how different rock types can change over geological time. In contrast, limestone is a sedimentary rock typically formed from the accumulation of marine organisms' remains, while sedimentary rocks are formed through the deposition and cementation of sediment. Igneous rocks result from the cooling and solidification of magma or lava. Thus, the distinct process of formation under heat and pressure is what categorizes metamorphic rocks and sets them apart from these other rock types.