Fe2+?Fe3+ ordered distribution in chromite spinels

Chen, Y. L.; Xu, B. F.; Chen, J. G.; Ge, Yuhua

doi:10.1007/bf00202316

Cited by 15 publications

(6 citation statements)

References 13 publications

(14 reference statements)

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“…Because of the high Cr concentration in Assemblee, we selected the values of δ and ΔE Q for chromite as constraints in the fitting procedures. The values we used are listed in Table 4, and they were obtained from a transmission MB spectrum of a terrestrial chromite sample we obtained at 293 K. The spectrum and parameters are similar to those reported by Chen et al [1992] for chromite spinels. These parameters worked well in the fitting procedures, giving both the chromite Fe 2+ and Fe 3+ subspectra (Figure 11); the relative subspectral areas of the two doublets was not constrained.…”

Section: Resultsmentioning

confidence: 91%

Evidence for montmorillonite or its compositional equivalent in Columbia Hills, Mars

Clark

Arvidson²,

Gellert

et al. 2007

J. Geophys. Res.

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[1] During its exploration of the Columbia Hills, the Mars Exploration Rover ''Spirit'' encountered several similar samples that are distinctly different from Martian meteorites and known Gusev crater soils, rocks, and sediments. Occurring in a variety of contexts and locations, these ''Independence class'' samples are rough-textured, iron-poor (equivalent FeO $ 4 wt%), have high Al/Si ratios, and often contain unexpectedly high concentrations of one or more minor or trace elements (including Cr, Ni, Cu, Sr, and Y). Apart from accessory minerals, the major component common to these samples has a compositional profile of major and minor elements which is similar to the smectite montmorillonite, implicating this mineral, or its compositional equivalent. Infrared thermal emission spectra do not indicate the presence of crystalline smectite. One of these samples was found spatially associated with a ferric sulfate-enriched soil horizon, possibly indicating a genetic relationship between these disparate types of materials. Compared to the nearby Wishstone and Watchtower class rocks, major aqueous alteration involving mineral dissolution and mobilization with consequent depletions of certain elements is implied for this setting and may be undetectable by remote sensing from orbit because of the small scale of the occurrences and obscuration by mantling with soil and dust.

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Section: Resultsmentioning

confidence: 91%

Evidence for montmorillonite or its compositional equivalent in Columbia Hills, Mars

Clark

Arvidson²,

Gellert

et al. 2007

J. Geophys. Res.

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“…QS values range from 0.7 to 2.3 mm/s with IS values of about 0.9 Journal of Geophysical Research: Solid Earth 10.1002/2017JB014363 to 1.1 mm/s. In staurolite, the reported QS and IS values for fourfold iron are 1.3 to 1.6 mm/s and~1 mm/s, respectively [Dowty, 1972], whereas in chromite, the fourfold ferrous iron has QS values ranging from 0.5 to 1.6 mm/s and IS values of 0.9 to 1.1 mm/s [Chen et al, 1992;Kuno et al, 2000]. Fourfold ferric iron has slightly higher QS values and significantly lower IS values than fourfold ferrous iron.…”

Section: Mössbauer Spectroscopymentioning

confidence: 99%

Electronic environments of ferrous iron in rhyolitic and basaltic glasses at high pressure

et al. 2017

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The physical properties of silicate melts within Earth's mantle affect the chemical and thermal evolution of its interior. Chemistry and coordination environments affect such properties. We have measured the hyperfine parameters of iron‐bearing rhyolitic and basaltic glasses up to ~120 GPa and ~100 GPa, respectively, in a neon pressure medium using time domain synchrotron Mössbauer spectroscopy. The spectra for rhyolitic and basaltic glasses are well explained by three high‐spin Fe2+‐like sites with distinct quadrupole splittings. Absence of detectable ferric iron was confirmed with optical absorption spectroscopy. The sites with relatively high and intermediate quadrupole splittings are likely a result of fivefold and sixfold coordination environments of ferrous iron that transition to higher coordination with increasing pressure. The ferrous site with a relatively low quadrupole splitting and isomer shift at low pressures may be related to a fourfold or a second fivefold ferrous iron site, which transitions to higher coordination in basaltic glass, but likely remains in low coordination in rhyolitic glass. These results indicate that iron experiences changes in its coordination environment with increasing pressure without undergoing a high‐spin to low‐spin transition. We compare our results to the hyperfine parameters of silicate glasses of different compositions. With the assumption that coordination environments in silicate glasses may serve as a good indicator for those in a melt, this study suggests that ferrous iron in chemically complex silicate melts likely exists in a high‐spin state throughout most of Earth's mantle.

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“…The first of these doublets has parameters corresponding to Fe 2+ in tetrahedral coordination, and we assign it to chromite [e.g., Osborne et al , 1981; Chen et al , 1992]. Work by Li et al [2002] on natural chromite reported three doublets with 298K parameters of δ = 0.97, 0.97, and 0.39 mm/s and Δ = 1.56, 0.90, and 0.56 mm/s respectively.…”

Section: Mössbauer Spectroscopymentioning

confidence: 99%

Martian Dunite NWA 2737: Petrographic constraints on geological history, shock events, and olivine color

et al. 2007

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[1] Meteorite Northwest Africa (NWA) 2737 is the second known chassignite, an olivine-rich igneous rock with mineral compositions and isotopic ratios that suggest it formed on Mars. NWA 2737 consists of $85% vol. olivine (Mg#, molar Mg/(Mg + Fe), of 78.3 ± 0.4%), which is notable because it is black in hand sample and brown in thin section. Other minerals include chromite, pyroxenes (augite, pigeonite, orthopyroxene), and diaplectic glass of alkali-feldspar composition. Aqueous alteration is minimal and appears only as slight dissolution of glass. NWA 2737 formed by accumulation of olivine and chromite from a basaltic magma; the other minerals represent magma trapped among the cumulus grains. Minerals are compositionally homogeneous, consistent with chemical equilibration in late and postigneous cooling. Two-pyroxene thermometry gives equilibration temperatures $1150°C, implying a significant time spent at the basalt solidus. Olivine-spinel-pyroxene equilibria give $825°C (possibly the T of mesostasis crystallization) at an oxidation state of $QMF-1. This oxidation state is consistent with low Fe 3+ in olivine (determined by EMP, Mössbauer spectra, and synchrotron micro-XANES spectroscopy) and with $10% of the iron in pyroxene being Fe 3+ . NWA 2737 experienced two shock events. The first shock, to stage S5-S6, affected the olivine by producing in it planar deformation features, intense mosaicism and lattice strain, and abundant droplets of iron-nickel metal, 5-15 nm in diameter. At this stage the olivine became deeply colored, i.e., strongly absorbing at visible and near-infrared (NIR) wavelengths. This shock event and its thermal pulse probably occurred at $170 Ma, the Ar-Ar age of NWA 2737. The colored olivine is cut by ribbons of coarser, uncolored olivine with long axes along [100] and shorter axes on {021} planes: These are consistent with the easy slip law for olivine [100]{021}, which is activated at moderate strain rate at high temperature. Within these ribbons the olivine was coarsened and the iron metal globules coalesced to micron-sized grains. The ribbons also are mosaicized and cut by planar fractures, which bespeak a second shock event, possibly that of ejection from Mars. The deeply colored olivine in NWA 2737 is unusual and represents a new ''ground truth'' type for remote sensing of Mars. Understanding the occurrence of the brown color in olivine in NWA 2737 places important constraints on interpretation of optical measurements.

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Fe2+?Fe3+ ordered distribution in chromite spinels

Cited by 15 publications

References 13 publications

Evidence for montmorillonite or its compositional equivalent in Columbia Hills, Mars

Evidence for montmorillonite or its compositional equivalent in Columbia Hills, Mars

Electronic environments of ferrous iron in rhyolitic and basaltic glasses at high pressure

Martian Dunite NWA 2737: Petrographic constraints on geological history, shock events, and olivine color

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