Metamorphic rocks are formed through a process called metamorphism, which involves the alteration of existing rocks due to high temperature, high pressure, or chemically active fluids. This process can change the mineral composition, texture, and overall structure of the original rock.
To understand this better, let’s consider the three main types of rocks: igneous, sedimentary, and metamorphic. When igneous or sedimentary rocks are subjected to intense heat and pressure beneath the Earth’s surface, they undergo changes that can result in the formation of metamorphic rocks. For instance, limestone, a sedimentary rock, can transform into marble, while shale, another sedimentary rock, can become slate.
Heat primarily comes from the Earth’s interior and can increase the temperature of the rocks. Pressure, on the other hand, is often due to tectonic forces, which can cause rocks to fold or even break. In addition, the presence of fluids can facilitate the movement of ions, which helps in recrystallization of minerals.
As a result of these processes, metamorphic rocks gain new characteristics, often becoming more dense and resilient. This transformation can take millions of years, and the final product of metamorphism reflects the original rock’s composition and the conditions it was subjected to.