X-ray diffraction and thermogravimetric studies have been carried out on iron precipitates obtained at different time intervals from Fe(II)-SO4-NH3-O-2 system. Depending on the experimental conditions amorphous and crystalline compounds were obtained. The iron content of the precipitates varied between 19.8 and 68%. The phases identified from X-ray diffractrograms were: hematite, goethite and magnetite. Qualitative indication was that the relative growth was in the order: hematite > goethite > magnetite. Thermogravimetric studies showed that for the crystalline precipitates, the weight loss decreased with the increase of precipitation time. In case of amorphous precipitates, the total weight loss (25 to 800 degrees C) passed through a minima for the sample collected at one hour interval. Based on the weight loss from precipitates in different temperature regions, probable nature of compounds has been proposed.