Metamorphic rock is a type of rock that forms when existing rocks, known as parent rocks, undergo changes due to high pressure, high temperature, or chemically active fluids. This process, called metamorphism, alters the mineral composition and structure of the original rock without melting it. Common examples of metamorphic rocks include schist, gneiss, and marble. Metamorphic rocks can be classified into two main categories: foliated and non-foliated. Foliated metamorphic rocks have a layered or banded appearance due to the alignment of minerals, while non-foliated rocks do not show this layering. These rocks are often found in regions that have experienced tectonic activity, such as mountain ranges.