All metamorphic rocks need this two factors so that they can be formed from either igneous or sedimentary rocks. The metamorphic rocks form deep into the ground where the pressure is higher and the temperature is higher as well, the deeper they form the bigger the pressure and temperature they experience. According to how big of a temperature and how big of a pressure the rocks have been exposed it determines into what type of metamorphic rocks they will turn into, and according to that what kind of a texture and appearance will they have. The amount of time of exposure to heat and pressure is also key to the type and quality of the metamorphic rocks.
