Which sedimentary rock is most likely to be changed to slate during regional memtamirpism?

Shale is the sedimentary rock most likely to be changed to slate during regional metamorphism. When subjected to increased pressure and temperature, the clay minerals in shale undergo recrystallization, resulting in the formation of slate, which exhibits a more foliated texture. This process typically occurs in areas with significant tectonic activity, where the conditions favor metamorphism.