The observed induction time for seeded gypsum crystallization was investigated with respect to gypsum particle seed size and mass loading. The induction time was significantly shortened in the presence of gypsum seeds (27-85 mu m) relative to unseeded solutions. The induction time correlated with the initial total seed surface area, suggesting that heterogeneous nucleation promoted by the added seeds is likely the governing mechanism responsible for shortening the observed crystallization induction time. The induction time also increased with increased magnesium ion concentration, but the effect diminished with increased initial gypsum seed area loading. The present study suggests that acceleration of desupersaturation of gypsum supersaturated solutions can be optimized with respect to the seed-added surface area with considerations of the inhibitory effect of magnesium on crystal nucleation and growth.