This work describes the formation at room temperature of finely dispersed crystalline iron-rich nickel ferrites, NixFe3-xO4, with x = 0, 0.10, 0.29 and 0.47, by precipitation in solutions containing constituent metal ions. Solids with x>0.47 consisted mostly of goethite, alpha-FeO(OH), in mixture with some ill-defined nickel compounds, even after the products were digested in the mother liquor at 100 degrees C. On calcination all solids had the spinel ferrite structure. Different physico-chemical properties of these powders are discussed, including their crystallinity, optical absorption in UV, visible, and far infrared ranges, and magnetic properties at room temperature, which depend strongly on the extent of Ni substitution.