Room-temperature magnetic properties of ferrihydrite: A potential magnetic remanence carrier?

Room-temperature magnetic techniques are rapidly becoming an important tool for the discrimination and quantification of minerals in a broad range of geological, environmental and extraterrestrial materials. The utility of these techniques is dependent upon the comprehensiveness and consistency of data describing the magnetic characteristics of individual mineral phases. In this regard, there is a paucity of data pertaining to the magnetic properties of ferrihydrite. This paper reports room-temperature magnetic properties of ferrihydrite that are relevant to studies concerning geological and environmental materials under surficial conditions. Synthetic ferrihydrite, both 2- and 6-line varieties, exhibit a susceptibility of ∼2.7 × 10− 6 m3 kg− 1 at 298 K. Significantly, at 298 K synthetic ferrihydrite exhibits a saturation remanent magnetization (σRS) of 1.19 and 0.86 × 10− 4 A m2 kg− 1 for 2- and 6-line ferrihydrite, respectively. These observations suggest that ferrihydrite is a potential magnetic remanence carrier under ambient environmental conditions. Measurements of mineral mixtures show that magnetic techniques can discriminate between ferrihydrite and goethite at low concentrations. Natural samples of ferrihydrite exhibit magnetic properties that are consistent with those obtained for synthetic ferrihydrite. Thus, magnetic techniques using room-temperature magnetic properties may find important applications in studies of the biogeochemical cycling of Fe in dynamic settings.