Abiotic Alteration of Goethite Nanoparticles

Abstract:

Goethite is a common iron-bearing mineral found in very diverse geological settings. It often occurs as particles made of nanoscale crystallites, which tend to increase its reactivity. At this meeting, we will present alteration experiments of nano-goethite particles after moderate heating in reducing or oxidizing atmospheres. Initial, intermediate, and final products of these experiments were characterized using low-temperature and room-temperature magnetometry, as well as non-magnetic techniques such as transmission electron microscopy and x-ray diffraction. Our results show that alteration of poorly crystalline nanophase goethite can produce strongly magnetic iron oxide nanoparticles. As a consequence, nano-goethite likely represents an important precursor of magnetic nanoparticles in the environment, which may impact a large number of paleoclimate, paleoenvironmental, and paleomagnetic studies. In particular, our experiments show that synthetic oriented aggregates of goethite nanoparticles can be easily converted to stoichiometric, highly crystalline, single-domain magnetite particles, including a substantial number of euhedral grains with morphologies similar to those of magnetosomes found in magnetotactic bacteria. Moreover, we demonstrate that such abiotic magnetite meets several of the biogenicity criteria commonly used for the identification of magnetofossils.