* Heat: The most important factor is heat. The heat can come from the Earth's interior (geothermal heat), or from the intrusion of magma. This heat causes the minerals in the sedimentary rock to recrystallize and change their structure.
* Pressure: Pressure, often from the weight of overlying rocks, can also cause the minerals to recrystallize and change their arrangement.
* Fluids: These fluids, often containing dissolved minerals, can react with the original sedimentary minerals and create new ones.
So, to summarize, the addition of heat, pressure, and sometimes fluids are the key factors that convert sedimentary rock into metamorphic rock.
