Environmental magnetism of nanophase iron minerals: Testing the biomineralization pathway

Nanoparticles of iron oxides and iron oxyhydroxides are sensitive proxies of environmental change near the earth's surface. Our research programme aims to provide information about the environmental control variables (temperature, rainfall, pH, as well as microbial type and concentration) for the process of Fe(III) to Fe(II) reduction and solid phase precipitation. Such solid phases of environmental change proxies (e.g., magnetite and maghemite) are being produced in the laboratory for calibration of field data. Low temperature magnetometry and Mössbauer spectra are shown to be extremely useful for characterization and granulometry of such nanophases. In addition, it appears that magnetism may also be a sensitive probe for physical–chemical properties of the outermost ‘skins’ of such nanoparticles, confirming Louis Néel's predictions for the magnetic behavior of such outermost layers.