The superparamagnetic Mössbauer spectra observed for ferrihydrite at room temperature are complex, and require fitting with at least two Lorentzian doublets to properly delineate the experimental data. Characteristic for such fits are a low (0.54 mm · s−1) and high (0.90 mm · s−1) quadrupole splitting. At 4K the Mössbauer spectrum of this mineral shows magnetic hyperfine splitting with a wide distribution of hyperfine fields, and a maximum absorption near 500 kOe.
Similar spectra are also shown by other iron oxides, especially hematite, of extremely small particle size (<100Å). This emphasizes basic structural relationships between the different iron oxides, but limits the applicability of Mössbauer spectroscopy as an analytical tool in this particle size range.