Which type of rock is created when an existing rock undergoes changes due to heat, pressure, or chemical reactions?

Metamorphic rock is formed through the transformation of existing rock types—either igneous, sedimentary, or even other metamorphic rocks—under conditions of high heat, pressure, and/or chemical processes. This process, known as metamorphism, alters the mineral composition and texture of the original rock without the rock completely melting.

The unique characteristic of metamorphic rocks is that they can display foliation (layering) or a non-foliated texture, depending on the degree of pressure and the mineral content involved. Examples of metamorphic rocks include schist, gneiss, and marble.

In contrast, igneous rocks are formed through the cooling and solidification of molten material (magma or lava), and sedimentary rocks are formed from the accumulation of mineral and organic particles, often in water. Residual rock is a term that refers to material left behind after processes like weathering and erosion, rather than a classification based on formation due to heat and pressure.