The effect of seeded nucleation on the formation and structural evolution of one-part ("just add water") geopolymer gels is investigated. Gel-forming systems are seeded with each of three different oxide nanoparticles, and seeding is shown to have an important role in controlling the silica release rate from the solid geothermal silica precursor, and in the development of physical properties of the gels. Nucleation accelerates the chemical changes taking place during geopolymer formation. The nature of the seeds affects the structure of the growing gel by affecting the extent of phase separation, identified by the presence of a distinct silica-rich gel in addition to the main, more alumina-rich gel phase. Synchrotron radiation-based infrared microscopy (SR-FTIR) shows the effect of nucleation on the heterogeneous nanostructure and microstructure of geopolymer gels, and is combined with data obtained by time-resolved FTIR analysis to provide a more holistic view of the reaction processes at a level of detail that has not previously been available. While spatially averaged (ATR-FTIR) infrared results show similar spectra for seeded and unseeded samples which have been cured for more than 3 weeks, SR-FTIR results show marked differences in gel structure as a result of seeding. (C) 2011 Elsevier Inc. All rights reserved.