This study describes the evolution of the nanoscale aqueous ferrous species as a function of the hydrolysis ratio and the influence of SiO4 ligands. Samples were synthesized under anoxic conditions and studied by EXAFS at the Fe K-edge. At low hydrolysis ratio (R = [OH-](added)/[Fe(II)](initial) = 0.1), the data are consistent with the formation of a planar Fe cluster with five Fe(II) octahedra. Although Si neighbors cannot be detected unequivocally by Fe K-edge EXAFS, they affect the condensation of ferrous species by hindering the linkages between Fe(II) octahedra. Indeed, at low hydrolysis ratio (R = 0.1) and Si/Fe = 1, only small sized Fe clusters such as planar Fe(II) trimers are formed. Moreover, this study clearly indicates that the polymerization of Fe(II) is more affected by the presence of SiO4 than in the case of Fe(III).