The effects of silica colloids on calcium sulfate dihydrate (gypsum, CaSO4 center dot 2H(2)O) crystallization are studied using feed solutions of varying degrees of supersaturation. A combination of light transmittance and electrical conductivity measurements is employed to characterize various aspects of the crystallization process. The induction time, nucleation rate, surface energy, and rate of crystallization of gypsum crystals are measured as functions of the saturation and the presence of noncrystallizing (SiO2) colloids. Scanning electron microscopy (SEM) imaging is used to characterize the morphology of formed crystals. The induction time and the rate of crystallization are both shown to increase when gypsum crystal formed from solutions containing suspended colloids. The findings are rationalized in terms of a mechanistic model that links the random motion of colloids with nucleation and crystal growth processes. The results have important implications for a variety of industrially relevant processes such as heat exchange and membrane separation and related fouling phenomena.