A series of fresh and 7 day aged Fe-Si samples have been investigated at the semilocal scale by small-angle X-ray scattering (SAXS), All the scattering curves are typical of amorphous aggregates. The subunits of the precipitates could not be determined precisely. However, the trend derived from SAXS modeling indicates that almost all the Fe is within subunits smaller than 7.5 Angstrom. The high fractal dimension (D-f) values of the aggregates ranging from about 2.0 to 2.7 are attributed to the presence of Si ligands. However, the value of D-f as a function of pH and Si concentration varies linearly with the polymerization state of iron.