The crystal growth kinetics of Cd5H2(PO4)(4),4H(2)O (PCDTP) was determined by mass crystallization experiments, in which pH was recorded at selected time intervals. A mixed mechanism of polynuclear surface nucleation and spiral growth was found. The Surface free energy calculated from the results agrees perfectly with the prediction by the Nielsen-Sohnel relation between solubility and surface energy. (C) 2002 Elsevier Science B.V. All rights reserved.