§ Meta: means many in Greek
§ Morph: means forms in Greek
§ Therefore Metamorphism means change in form.
§ Metamorphic rock forms when existing rock are exposed to tremendous heat, great pressure and chemical reactions deep in the mantle and causes them to change into different rocks.
§ Metamorphic rock can be formed from any existing rock: sedimentary, igneous or metamorphic already.
§ During metamorphism a rock’s texture and chemical structure is changed.
§ They are classified by texture (in metamorphic rock it is the arrangement of crystals):
oFoliated: Crystals are arranged in bands or layers and break along those bands.
Foliated means leaf in Latin. The layers in foliated rocks are thin and flat like leaves. Most metamorphic rocks are foliated.
Examples are: Schist, Slate and Gneiss.
o Unfoliated: They do not contain bands or layers. Less popular.
Examples are: Quartzite and Marble.
Examples of metamorphic changes to existing rocks: