Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31c1714o&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P31C-1714
Other
[3625] Mineralogy And Petrology / Petrography, Microstructures, And Textures, [3672] Mineralogy And Petrology / Planetary Mineralogy And Petrology, [3929] Mineral Physics / Nmr, Mossbauer Spectroscopy, And Other Magnetic Techniques, [3954] Mineral Physics / X-Ray, Neutron, And Electron Spectroscopy And Diffraction
Scientific paper
Maghemite (γ-Fe2O3) can form in hydrothermal environments during the transformation of magnetite (FeO)(Fe2O3) into hematite (α-Fe2O3), known as martitisation. Understanding the martitisation process will give important information on the temperature and oxygen availability during rock formation and transformation on Earth, but also for the Martian surface layer, which is significantly richer in iron than Earth. Two martites (from the 2.9 Ga, Dhawar Craton banded iron formation, India and an octahedral martite from the Espinhaço Range, Brazil) were investigated by optical microscopy, SEM-FIB-TEM, Raman and 57Fe Mössbauer spectrometry, X-ray-diffraction and for its magnetometry, Curie Balance and hysteresis. Both martites are mainly composed of hematite hosting magnetite relicts. The Indian martite is characterized by a trellis pattern. A FIB-cut in a single crystal of magnetite from the Brazilian martite reveals an area rich in dislocations and zones of diffraction contrast of ~5 nm, representing high and low-stoichiometric volumes. Selected area electron-diffraction patterns of these non-stoichiometric volumes show splitting of the major intensities suggesting that at least two crystals are present. Those with the highest intensities correspond to magnetite. The second (split intensities) can be attributed to a crystal with the same cubic system as magnetite with smaller lattice parameters, which might indicate a shrinking of the crystal lattice due to a Fe2+ loss and with the formation of vacancies giving rise to non-stoichiometry zones, ranged from ideal magnetite and maghemite, resulting from oxydation process. In the Indian martite, a FIB-cut at a magnetite-hematite interface exhibit TEM images and selected area electron diffraction patterns of subhedral lamellar crystals of intergrown magnetite and maghemite, and interstitial crystals, without lamellae, of hematite. The sharp contact between the two crystals represents an oxidation-exsolution process that produces the trellis pattern. The presence of maghemite in the Brazilian martite is confirmed by Raman spectrometry. It is suspected in Curie Balance curves, with a slight decrease in magnetisation just below 400°C, the wasp-waist magnetic hysteresis loops and XRD patterns. In the Indian sample the presence of maghemite is confirmed by Mössbauer spectrometry. Our results allow us to conclude that the two investigated martites both most likely contain maghemite that is present in the relict magnetite either as nanocrystals and/or as an intermediate phase. However the two martites show different features, non-stoichiometric volumes were only observed in the Brazilian martite, while lamellae and non-lamellae structures were only observed in the Indian martite. These features might influence the contrasting results obtained by the other analytical methods.
Fabris J. D.
Greneche J.
Morgan Rhonda
Orberger Beate
Tudryn A.
No associations
LandOfFree
The presence of maghemite in martite: implications for the interpretation of data from the Mars Science Laboratory does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The presence of maghemite in martite: implications for the interpretation of data from the Mars Science Laboratory, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The presence of maghemite in martite: implications for the interpretation of data from the Mars Science Laboratory will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-870255