What Rocks Can Be Metamorphic?
Metamorphic rocks are actually pre-existing rocks that were altered from one form to another under the influence of excessive heat, pressure or through the chemical action of certain liquids. For instance, shale is converted into lime stone and slate which in turn changes into marble. By virtue of alteration caused by metamorphism, there are structural and chemical modifications made to the minerals which constitute the rock. The pre-existing rocks can be sedimentary, igneous or even metamorphic rocks. Most of the continental crust on the Earth is made up of igneous and metamorphic rocks. Some of the oldest rocks found on planet earth (as old as 4 billion years) are metamorphic. Some of the types of rocks found on the various mountain ranges are also metamorphic in nature.
