Which type of rock undergoes transformation due to heat and pressure?

Metamorphic rock is formed through the transformation of existing rock types—either sedimentary or igneous—under conditions of intense heat and pressure. This process, known as metamorphism, alters the mineral composition and structure of the rock without the rock melting.

For example, limestone, a sedimentary rock, can transform into marble when subjected to heat and pressure, whereas granite, an igneous rock, can change into gneiss under similar conditions. Metamorphic rocks exhibit characteristics such as foliation or banding and can often have various mineral types that speak to their parent rock and the specific conditions they underwent.

In contrast, sedimentary rocks are typically formed from the accumulation of particles, organic material, and mineral precipitation and do not transform directly due to heat and pressure; they instead represent a different stage of rock formation. Igneous rocks form from the solidification of molten material and are not products of metamorphism. While all rock types form part of the rock cycle, metamorphic rocks are specifically defined by their process of transformation through heat and pressure in the context of this question.