Magnetite

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

Changes of ferromagnetic minerals and their bearing on magnetic properties of rocks

Abstract: Physical and chemical properties of samples from a group of pre-Cambrian diabase dikes characterized by an inverse magnetization have been determined. There are present two different ferromagnetic minerals intimately intermingled with one another and with non-magnetic ilmenite. Experiments to duplicate the original thermomagnetic behavior of these rocks cannot be carried out because by heating, non-reversible changes of physical structure are produced which alter the magnetic properties of the sample. Magnetization experiments show that the inverse magnetization is produced by particles having high coercive force; in natural samples a large part of the ferromagnetic material is demagnetized but can be easily magnetized. The hypothesis is advanced that the inverse magnetizations of these dikes having uniform magnetization could have been produced with the earth's magnetic field in its present-day sense, as a result of the partial low-temperature oxidation of primary magnetite forming small particles of high coercive force in the reversed induction field adjacent to large magnetite particles and the subsequent demagnetization of some of the larger particles. Various implications of the hypothesis are pointed out. The gross scattering of directions of magnetization observed in two dikes are proved not to have been caused by turbulent movements below the Curie point; the scatter is attributed to chemical changes, but no detailed mechanism for producing the scatter is proposed.

Experimental diagenesis of organo-mineral structures formed by microaerophilic Fe(II)-oxidizing bacteria

Abstract: Twisted stalks are organo-mineral structures produced by some microaerophilic Fe(II)-oxidizing bacteria at O2 concentrations as low as 3 μM. The presence of these structures in rocks having experienced a diagenetic history could indicate microbial Fe(II)-oxidizing activity as well as localized abundance of oxygen at the time of sediment deposition. Here we use spectroscopy and analytical microscopy to evaluate if--and what kind of--transformations occur in twisted stalks through experimental diagenesis. Unique mineral textures appear on stalks as temperature and pressure conditions increase. Haematite and magnetite form from ferrihydrite at 170 °C-120 MPa. Yet the twisted morphology of the stalks, and the organic matrix, mainly composed of long-chain saturated aliphatic compounds, are preserved at 250 °C-140 MPa. Our results suggest that iron minerals might play a role in maintaining the structural and chemical integrity of stalks under diagenetic conditions and provide spectroscopic signatures for the search of ancient life in the rock record.

Electrochemical Growth of Diverse Iron Oxide (Fe3O4, α-FeOOH , and γ-FeOOH) Thin Films by Electrodeposition Potential Tuning

Abstract: Magnetite, goethite, and lepidocrocite thin films have been electrochemically grown on titanium substrates by the anodic oxidation of ferrous ions in a 0.01 M FeSO 4 (NH 4 ) 2 SO 4 ·6H 2 O + 0.04 M CH 3 COOK, pH 6.0, aqueous solution. It is demonstrated that the deposition potential can be used as a tool to tune the obtainment of the different pure phases of the iron oxide-oxyhydroxides thin films. Results of an exhaustive structural characterization, a morphological study, and X-ray photoelectron spectroscopy characterization are presented.