A metamorphic rock can turn into an igneous rock if it becomes hot enough to melt. Then, when it cools enough to become solid the result will be an igneous rock. An igneous rock can become metamorphic, if it is under pressure when it is heated. The pressure will keep the rock from melting but will allow the atoms to unite with our atoms forming new minerals when the rock cools. The resulting metamorphic rock will have some new minerals that the igneous didn't have. The new minerals will have a ordered physical arrangement unlike the random mixture of an igneous rock.
