Under these conditions of pressure and temperature, the minerals that are part of the original rock are transformed into different ones, which originates a new rock, the metamorphic rock. Only a rearrangement of the atoms that form the minerals occurs, so the chemical composition of the metamorphic rock is the same as that of the rock from which it comes.
Metamorphism is the set of changes that occur in the rock, without reaching fusion, when the rock is subjected to different temperature or pressure conditions than those that originated it. The resulting rock is called metamorphic rock.
For example, from the sedimentary rock clay the metamorphic rock slate is obtained; from igneous rock granite is obtained from the metamorphic rock gneiss, and marble is obtained sedimentary rock limestone.