The influence of AI on the products formed by aerial oxidation at pH 5.5--7 and 20~ of FeOI) chloride, sulfate and carbonate solutions, was examined. In all cases AI at levels AI/AI + Fe = 0.09--0.30 inhibited the formation of y phases (lepidoerocite and maghemite) in favor of goethite under conditions where, in the absence of AI, these 3' phases formed. The influence of AI in these laboratory studies was supported by field observations. At higher levels of A1, ferrihydrite formation was favored. This effect of AI was seen to be the result of a slowing down in the hydrolysis/oxidation rate of the Fe(II) system.The presence of A1 not only changed the direction of mineral formation, but also caused the formation of A1 substitued goethites which resembled in particle size and morphology the natural aluminiferous goethite extracted from a soil.