Process of Exfoliation / Onion Weathering
Exfoliation is a kind of mechanical / physical weathering. Hot sunlight heats up rock surface and causes expansion during day-time. The rapid heat loss will cause contraction at night. Due to poor conduction, the contrast in temperature is much greater on the surface layer of the rock than at the inner part. Greater expansion and contraction will finally lead to the peeling off of the outer layer.