Magnetite

About: Magnetite is a research topic. Over the lifetime, 10277 publications have been published within this topic receiving 278071 citations.

Magnetic properties of hydrothermally recrystallized magnetite crystals.

Abstract: The discrepancy between the magnetic hysteresis properties of magnetite crystals that are precipitated from solution ( 0.3 micrometer) is not an inherent property of magnetite but is caused by the highly stressed state of crushed material and by adhering finer fragments. The size trends of magnetic properties exhibited by submicrometer-size precipitated grains continue in the size range from 1 micrometer to 1 millimeter in a set of hydrothermally recrystallized magnetite crystals. Coercive forces of these narrowly sized crystals follow a power law over a wide size range (0.1 micrometer to 1 millimeter) as predicted by theory. Dislocation etch pits show similar dislocation densities for hydrothermally grown (3 x 1010 meter -2) and natural (1 x 1010 meter-2) magnetite crystals. Hysteresis parameters of hydrothermally grown crystals are similar to those of natural crystals but are about one-fifth of those for crushed grains.

Magnetite diagenesis in marine sediments from the Oregon continental margin

Abstract: The magnetochemistry of sediments from the Oregon continental margin is examined to determine the effects of iron-sulfur diagenesis on the paleomagnetic record Magnetic mineral dissolution and transformation into iron sulfides are a common feature in these suboxic to anoxic lutites These processes are evidenced in rapid decreases in natural remanent magnetization intensities and stabilities, systematic changes in other rock magnetic properties, and increases in solid phase sulfur concentrations with depth Hysteresis measurements are used to evaluate downcore changes in magnetite concentration and grain size Magnetite abundances decrease downcore from initial values of about 01%, and nominal grain diameters lie within a narrow pseudosingle domain range of 008 to 06 μm A first-order surface area reaction model, dA/dt = -kA, is proposed to explain the magnetite dissolution mechanism, where A is the total magnetite surface area and k is the rate constant The solution of this equation predicts that the surface area and concentration decrease exponentially, and the concentration, in addition, depends on grain size Application of this model in two cores where grain size varies with depth successfully explains the downcore profiles of both concentration and surface area Despite extensive magnetite destruction, magnetic directions in such sediments appear to reliably record long-wavelength trends of the geomagnetic field

Lizardite versus antigorite serpentinite: Magnetite, hydrogen, and life(?)

Abstract: The serpentinization of peridotite operates according to one or the other, or a combination, of two end-member mechanisms. In low-temperature environments (50–300 °C), where lizardite is the predominant serpentine mineral, olivine is consumed by reaction with H2O but its composition (Mg#) remains unchanged. Mg-rich lizardite, magnetite, and dihydrogen gas (±brucite) are products of the reaction. At higher temperatures (400–600 °C), rates of MgFe diffusion in olivine are orders of magnitude faster, with the result that the growth of Mg-rich antigorite can be accommodated by a compositional adjustment of olivine, eliminating the need to precipitate magnetite and evolve hydrogen. This latter end-member mechanism probably best reflects the situation in the forearc mantle wedge.