Fused silica platelets were implanted or coimplanted with sodium, magnesium, and aluminum and annealed in 1 atm flowing oxygen at 900degreesC. Concentration depth profiles of these elements in the implanted samples were obtained using secondary ion mass spectrometry before and after the annealing treatment. The presence of fast-moving sodium markedly accelerated the diffusion of magnesium in silica. Incorporation of aluminum in silica significantly retarded the diffusion of sodium and magnesium. This study yielded valuable information for the understanding of the roles of various grain-boundary cations in oxidation of silica-forming ceramics.