In situ atomic force microscopic studies of brushite dissolution suggest an exactly analogous mechanism to that of crystallization in which embryo formation takes place only after critical conditions are reached. Experimentally, the relationship between the spreading rate of dissolution steps and their sizes is first measured and the elimination of active dissolution sites is observed at different undersaturations. The results reinforce our previous "self-inhibition" model in which the dissolution rates decrease with time and the reactions are effectively suppressed. The data suggest a metastable zone for dissolution in undersaturated solutions, and this is confirmed by constant composition dissolution experiments near equilibrium. Clearly, it is important to understand the mechanism of dissolution when attempts are made to measure, experimentally, the solubilities of sparingly soluble minerals. Surface dissolution pits not only play important roles in dissolution kinetics, but also they can directly influence crystal morphology.