Browsing by Author "University of Minnesota Institute for Rock Magnetism"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item Data for "Late Paleozoic depositional environments and sediment transport directions of the Itararé Group rocks from the state of São Paulo, Brazil, determined from rock magnetism and magnetic anisotropy" collected at the University of Sao Paulo and the University of Minnesota between 2012 and 2020.(2020-12-22) Bilardello, Dario; dario@umn.edu; Bilardello, Dario; University of Minnesota Institute for Rock MagnetismItem Data for "Simulation of natural alteration of iron oxides in soil: conversion of synthetic ferrihydrite to hematite without artificial dopants, observed with magnetic methods" collected at the University of Minnesota between 2016 and 2020(2020-03-12) Bilardello, Dario; Banerjee, Subir K; Volk, Michael; Soltis, Jennifer A; Penn, R. Lee; dario@umn.edu; Bilardello, Dario; University of Minnesota Institute for Rock MagnetismWe present the results of a new study on the conversion of pure, undoped synthetic ferrihydrite, wet-annealed at pH 6.56 and 90 ℃ without stabilizing ligands, to nanophase goethite, hematite and an intermediate magnetic phase, likely to be nanophase maghemite. Our analysis included magnetic field and temperature dependent properties and characterization by powder x-ray diffraction, Mössbauer spectra and high-resolution transmission electron microscopy. Unlike most other studies of ferrihydrite alteration we sampled alteration products after 0.5 hours, and then in a geometric progression to 32 hours, yielding an extremely detailed examination of the earliest alteration phases. There are many similarities to the latest studies of pure ferrihydrite alteration but with a significant difference: we observe very early appearance of oriented nanophase goethite along with a soft magnetic contribution, while rhombohedral hematite crystals are formed later, as reported in the previous studies. Our observations attest to the non-uniqueness of the magnetic enhancement process and to its strong dependence on environmental conditions, with important implications for the proposed hematite/goethite ratio as a reliable proxy for paleoprecipitation intensity.