Parent rocks, also known as protoliths, are the original rocks from which metamorphic rocks are formed. These rocks can be igneous, sedimentary, or even other metamorphic rocks. When subjected to heat and pressure over time, the minerals and textures of the parent rock change, resulting in a new type of rock with different characteristics. For example, limestone can become marble when it undergoes metamorphism. The transformation process alters the rock's structure and mineral composition, creating unique features. Understanding parent rocks is essential for geologists as it helps them trace the history and evolution of the Earth's crust.