The crystal structure of two-phase and porous alkali borosilicate glasses with embedded magnetic atoms has been investigated using X-ray powder diffraction. It has been shown that, during the preparation of two-phase (nonporous) glasses, the α-Fe2O3 phase undergoes a transition to magnetite (Fe3O4) with the formation (at particular concentrations of α-Fe2O3 in the initial mixture) and stabilization of the β-Fe2O3 phase. The characteristic sizes of nanoparticles of iron oxides (Fe3O4 and β-Fe2O3) in these glasses have been determined. For two types of porous glasses (namely, the macroporous glass Fe20-MAP and the microporous glass Fe20-MIP), the occupancies of the octahedral (Fe2+) and tetrahedral (Fe2+/Fe3+) iron positions in magnetite have been found.