One of the three major rock types, metamorphic rock is created through the heating and pressurizing of rock. Metamorphic processes can happen deep within the Earth or from continental collisions or other tectonic processes. Gneiss, slate, marble, and schist are a few types of metamorphic rock. Metamorphic rocks are defined as either foliated or non-foliated. The minerals in foliated metamorphic rocks separate and create bands of different minerals during the cooling process. Non-foliated metamorphic rocks, such as marble, don’t show any banding. Colorado’s state rock is Yule Marble, a non-foliated metamorphic rock.