How is a metamorphic rock formed?

A metamorphic rock is formed through the transformation of existing rocks due to the influence of heat, pressure, or chemical reactions. This process, known as metamorphism, occurs deep within the Earth's crust, where temperatures and pressures are significantly higher than at the surface. During metamorphism, the minerals within the original rock can change chemically and physically without the rock melting, resulting in a new rock type with distinct characteristics.

For example, shale, a sedimentary rock, can transform into schist, a metamorphic rock, when subjected to sufficient heat and pressure over time. This change often leads to foliation, where the minerals align in specific directions, creating a layered appearance. The correct answer highlights this crucial aspect of the metamorphic rock formation process, distinguishing it from other rock types formed by different mechanisms.