The type of rock that forms from an existing rock that is altered by heat, pressure, or chemical reactions is called a metamorphic rock. Metamorphic rocks originate from pre-existing rocks, which can be either igneous, sedimentary, or even other metamorphic rocks.
During the process of metamorphism, the original rock, known as the ‘parent rock’ or ‘protolith,’ undergoes significant changes. These changes can occur due to increased temperature and pressure, often associated with tectonic activity, or through the influence of chemically active fluids. The mineral composition, texture, and structure of the original rock are transformed, leading to the formation of new minerals and a new texture.
For example, limestone, which is a sedimentary rock, can metamorphose into marble when subjected to high heat and pressure. Similarly, shale, another type of sedimentary rock, can change into schist or gneiss under similar conditions. The fascinating aspect of metamorphic rocks is that their characteristics can provide insights into the geological history and conditions that prevailed in the Earth’s crust during their formation.