M�ssbauer study of a California desert celadonite and its pedogenically-related smectite

Bowen, L. H.; DeGrave, E.; Reid, David A.; Graham, Robert C.; Edinger, S. B.

doi:10.1007/bf00223320

Cited by 14 publications

(13 citation statements)

References 24 publications

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“…The value of d I is~0.58 mm/s for Fe 3+ and 1.31 mm/s for Fe 2+ across all models and line shapes. Our results are fairly similar to those calculated for celadonite (another dioctahedral mica) by Bowen et al (1989), who found d 0 = 0.61À0.70 mm/s for Fe 3+ and d 0 = 1.35 mm/s for Fe 2+ .…”

Section: Intrinsic Isomer Shift and Mössbauer Temperaturesupporting

confidence: 91%

Mössbauer spectroscopy of phyllosilicates: effects of fitting models on recoil-free fractions and redox ratios

Dyar¹,

Schaefer²,

Sklute³

et al. 2008

Clay miner.

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Clay minerals are ubiquitous constituents in soils on Earth, are occasionally found in meteorites, and may also occur on planetary surfaces in the presence of water. However, little is known about the fundamental Mössbauer parameters (the intrinsic isomer shift, δI, the characteristic Mössbauer temperature, θM, and the recoil-free fraction, f) that are characteristic of clay minerals and critical to the correct interpretation of the Fe3+/ΣFe ratios as well as the mineral modes. Spectra of well characterized single mineral samples at multiple temperatures may be used for the determinations of f. Hence, measurements of five-layer silicates with a range of layer types are presented here: nontronite, Fe-smectite, glauconite, annite and biotite. The spectra were fitted using three different software packages: WMOSS from Science, Engineering & Education Co. in Minnesota; Recoil, from the University of Ottawa in Canada; and two programs used at the University of Ghent in Belgium. Four different approaches to modelling line shapes were used: (1) Lorentzian; (2) pseudo-Voigt (convolution of Lorentzian and Gaussian curves); (3) quadrupole-splitting distributions (QSD); and (4) a technique that does not assume a particular line shape (subsequently referred to as ‘model-independent’). Values of δI, θM and f were determined using the method of De Grave & Van Alboom (1991).Results show that multiple doublets are routinely required by all models to represent Fe-site occupancy, even when all the Fe atoms of the same valence are in the same site, as is the case for dioctahedral smectite, nontronite, mica and glauconite. Consistent values of centre shift (δ) and quadrupole splitting (Δ) were obtained for the two distributions of M2Fe3+ in the smectites. In glauconite, a single Fe2+ doublet was clearly resolved and gave systematic values for δ, Δ and area, but the two Fe3+ doublets were less defined. In annite, two Fe2+ and two Fe3+ doublets were modelled, while three Fe2+ and one Fe3+ doublet were used for biotite. Three different programs that use Lorentzian line shapes gave very similar results for δ, Δ and area. The two different implementations of QSD line shapes gave similar but sometimes slightly different results, and the pseudo-Voigt and model-independent fits usually fell between the ranges for Lorentzian and QSD results.The value of δI is ~0.58 mm/s for Fe3+ and ~1.31 mm/s for Fe2+ across all models and line shapes, which is expected because the Fe3+ has an additional shielding 3d electron. Values for θM data are nearly identical for Fe3+ in nontronite and Fe-smectite (~450 K), somewhat varied for Fe3+ in glauconite and biotite (θM = ~730 K and ~615 K, respectively), and relatively distinct for Fe2+ (~350 K). Some values for θM and f could not be determined due to the non-monotonic behaviour of the fitted values for δ as a function of temperature. Values of f295 were 0.821–0.917 for Fe3+ and 0.662–0.743 for Fe2+, consistent with previous studies of the recoil-free fraction in micas and other silicates. Calculated scatter in δ, Δ, area and f values as a function of different line shapes and computer software was significantly reduced at lower temperatures. Sources of error in each of the calculated parameters are discussed.

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Section: Intrinsic Isomer Shift and Mössbauer Temperaturesupporting

confidence: 91%

Mössbauer spectroscopy of phyllosilicates: effects of fitting models on recoil-free fractions and redox ratios

Dyar¹,

Schaefer²,

Sklute³

et al. 2008

Clay miner.

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“…A doublet corresponding to Fe 3+ in jarosite could be identified in the Mössbauer spectra of all ten of these samples ( Figure 5 and Data Sets 1 and 2). 1 A second doublet is present in all fifteen samples and is consistent with Fe 3+ in dioctahedral phyllosilicates such as glauconite, celadonite and/or nontronite [Daynyak and Drits, 1987;Reid et al, 1988;Bowen et al, 1989;Drits et al, 1997]. It is possible that nanophase, i.e., superparamagnetic Fe (hydr)oxides contribute to this doublet.…”

Section: Mössbauer Resultsmentioning

confidence: 56%

“…The sextet identified in sample 08-T34 is also consistent with an Fe-(oxyhydr)oxide, possibly superparamagnetic or Al-substituted goethite (a-FeOOH). These [Daynyak and Drits, 1987;Reid et al, 1988;Bowen et al, 1989;Drits et al, 1997] or possibly stevensite. Reid et al [1988] and Bowen et al [1989] documented the pedogenic alteration of celadonite into an Fe-rich smectite upon the release of interlayer K + ions.…”

Section: Mössbauer Resultsmentioning

confidence: 99%

Jarosite in a Pleistocene East African saline-alkaline paleolacustrine deposit: Implications for Mars aqueous geochemistry

McHenry

Chevrier²,

Schröder

2011

J. Geophys. Res.

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[1] Jarosite occurs within altered tephra from the saline-alkaline paleolake deposits of Pliocene-Pleistocene Olduvai Gorge, Tanzania. Zeolites (mainly phillipsite), authigenic K-feldspar, and Mg/Fe-smectites dominate the mineral assemblage, indicating salinealkaline diagenetic conditions (pH > 9). As jarosite is ordinarily an indicator of acidic conditions on Earth and Mars, its association with such undisputed high-pH indicators is unexpected. Of 55 altered tephra samples collected from the paleolake basin and margin deposits, eleven contained jarosite detectable by X-ray Diffraction (XRD) (>0.15%). Mössbauer spectroscopy, Fourier Transform Infrared Reflectance (FTIR), Electron Probe Microanalysis (EPMA), X-ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM) analyses confirm the presence and nature of the jarosite. This paper documents this occurrence and presents mechanisms that could produce this unusual and contradictory mineral assemblage. We favor a mechanism by which jarosite formed recently, perhaps as modern ground and meteoric water interacted with and oxidized paleolacustrine pyrite, providing local and temporary acidic conditions. However, local groundwater (at modern springs) has a pH > 9. In recent studies of Mars, the presence of jarosite or other Fe or Mg sulfates is often used to indicate dominantly acidic conditions. Regardless, the current study shows that jarosite can form in sediments dominated by alkaline minerals and solutions. Its coexistence with Mg/Fe smectites in particular makes it relevant to recent observations of Martian paleolakes.Citation: McHenry, L. J., V. Chevrier, and C. Schröder (2011), Jarosite in a Pleistocene East African saline-alkaline paleolacustrine deposit: Implications for Mars aqueous geochemistry,

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“…For a four-fold coordination in a given compound the iron-oxygen bond length is usually shorter than for the six-fold coordination in that compound. On the other hand, the total bond strength in the latter Bowen et al (1989);9 = De Grave and Vochten (1985); 10 = Ellwood et al (1989) is increased by the higher coordination number. In spinel oxides the ferric ions on tetrahedral sites generally exhibit a higher OM value as compared to that for the octahedral sites (Vandenberghe and De Grave 1989).…”

Section: Resultsmentioning

confidence: 88%

Evaluation of ferrous and ferric Mössbauer fractions

1991

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Abstract. The M6ssbauer fractionsffor various ferrousand/or ferric-containing oxides and oxyhydroxides, silicates and carbonates were evaluated from the experimental temperature dependence of their center shifts, using the Debye approximation for the second-order Doppler shift. It is concluded that ferrous ions exhibit a lower fraction as compared to ferric ions. Using standard mixtures of e-F%O3 with selected Fe z + or Fe 3 + compounds, it is found that the calculated Fe 3 + fvalues are somewhat overestimated with respect to those of Fe 2 +. Possible explanations for this shortcoming are discussed and it is suggested that a different temperature dependence of the intrinsic isomer shift is the most likely reason. This suggestion is corroborated by analyses of hematite and hedenbergite data which are available for temperatures up to 900 K and 800 K respectively.

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M�ssbauer study of a California desert celadonite and its pedogenically-related smectite

Cited by 14 publications

References 24 publications

Mössbauer spectroscopy of phyllosilicates: effects of fitting models on recoil-free fractions and redox ratios

Mössbauer spectroscopy of phyllosilicates: effects of fitting models on recoil-free fractions and redox ratios

Jarosite in a Pleistocene East African saline-alkaline paleolacustrine deposit: Implications for Mars aqueous geochemistry

Evaluation of ferrous and ferric Mössbauer fractions

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