Of the 3 basic rock types, the type that was once one form but has changed to another due to heat & pressure
[DOC] [TLE] Formation of rocks - Wikipedia [PAR] Metamorphic rocks are rocks which once existed as igneous or sedimentary 
rocks but have been subjected to varying degrees of pressure and heat within the
... [DOC] [TLE] metamorphic rocks - Math/Science Nucleus [PAR] types of rocks can change into another type of rock.