Part of Hall of Planet Earth.
Metamorphic rocks form when sedimentary, igneous, or pre-existing metamorphic rocks are changed by heat, pressure, and chemically reactive waters. These rocks are identified by their minerals and texture.
During metamorphism, new minerals grow, with different sizes, shapes, and orientations than those of the original minerals. The chemical composition of the original rock may also change, as some elements are carried away and others are added by the fluids flowing through the rocks.