The Collaborative International Dictionary of English v.0.48:

Exfoliation \Ex*fo`li*a"tion\, n. [Cf. F. exfoliation.]
   The scaling off of a bone, a rock, or a mineral, etc.; the
   state of being exfoliated.
   [1913 Webster]

WordNet (r) 3.0 (2006):

exfoliation
    n 1: the peeling off in flakes or scales of bark or dead skin;
         "exfoliation is increased by sunburn"
    2: a thin flake of dead epidermis shed from the surface of the
       skin [syn: scale, scurf, exfoliation]