Within the Earth, rocks can be changed by heat, pressure or both. Minerals in the rocks break down and re-form in different combinations, altering the appearance and properties of the rocks. This process of change is called metamorphism.
There are two types of metamorphism, contact and regional.
Rocks surrounding a mass of magma can become so hot they are ‘cooked’ and new minerals form. This process is called contact metamorphism.
When continents collide, great thicknesses of rocks are buried, compressed and heated. The resulting change affecting large volumes of rocks is called regional metamorphism.