The crystallization process of MgO-CaO-SiO2-Na2O glasses in the presence of CaF2 and MoO3 nucleating agents was investigated by DTA, XRD and SEM. The effect of compositional changes on bulk crystallization and growth morphology has been studied. After a two-stage heat treatment, the phases such as wollastonite, diopside and cristobalite, were identified. The ability of CaF2 and MoO3 pair as nucleating agents in inducing bulk nucleation in these glasses was attributed to the surface tension and viscosity reductions. The observed pore formation phenomenon upon the increase of MgO content in these glass-ceramics was related to the difference in density between the residual glass and diopside as the main crystalline phase. (C) 2003 Kluwer Academic Publishers.