Soda alumina borosilicate glasses of composition (24-y)Na2O center dot yAl(2)O(3)center dot 14B(2)O(3)center dot 37SiO(2)center dot 25Fe(2)O(3), y = 8, 12, 14, 16 mol%, were melted using Fe2O3 as raw material. Besides, samples with y = 12 and Fe2O3 concentrations of 14.32, 17.8, and 25.0 mol% were prepared from FeC2O4 center dot 2H(2)O as raw material. The X-ray diffraction analyses showed the presence of magnetite for the samples from all the investigated compositions. Transmission electron microscopy (TEM) evidenced that all the samples are phase separated and droplets in the diameter range 100-1000 nm, enriched in iron, are formed. Inside these droplets, numerous small magnetite particles, with size in the 25-40 nm interval, are crystallized.