Precipitation of calcium tripolyphosphate (CaTPP) from strongly supersaturated solution is accompanied by tripolyphosphate hydrolysis if the bulk Ca/TPP mole ratio is in excess of about 2. Along with the tendency for hydrolysis, a change in the crystal habit from crystalline to amorphous is observed beyond this bulk ratio. The composition of the material changes as well from mainly Ca2NaP3O10 at a 2:1 Ca/TPP bulk ratio to Ca-5(P3O10)(2) at an 8:1 bulk ratio, though the water of hydration contents are similar. The crystallinity change is reflected in the IR and solid-state P-31 NMR spectra, but, beyond these expected differences, the amorphous samples also appear to have a larger fraction of more mobile crystal water. Through a series of sequential experiments, it was identified that hydrolysis of these materials mainly occurs via a mechanism consisting of precipitation of CaTPP followed by hydrolysis of the precipitate. Bulk water does not play a critical role in the hydrolysis nor does surface adsorbed water, to the extent that it can clearly be differentiated from the crystal or bound water. Kinetic studies of the hydrolysis of the 8:1 material showed that its solid-state reaction rate (7.1 x 10(-3) min(-1) at 70 degrees C) is 2 orders of magnitude higher than that of NaTPP. The hydrolysis mechanism is found to lay midway between first order and diffusion controlled, leading us to suspect that loosely bound water within the crystal lattice constitutes the diffusing species. Although the facile hydrolysis at the stronger supersaturation can possibly be explained in terms of the higher Ca/TPP ratio in the precipitate leading to destabilization of the P-O-P bond, the observed trends seem to rather suggest the diffusion of crystal water within the strongly distorted crystal lattice as the dominant factor.