Iron oxidation state in the Fe‐rich layer and silica matrix of Libyan Desert Glass: A high‐resolution XANES study

Giuli, Gabriele; Paris, Eleonora; Pratesi, Giovanni; Koeberl, Christian; Cipriani, Curzio

doi:10.1111/j.1945-5100.2003.tb00306.x

Cited by 62 publications

(51 citation statements)

References 17 publications

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“…By extracting the pre-edge peak centroid and the integrated intensities (given in Table 2), these data can be compared with those of the model compounds with known Fe oxidation state and coordination number (Wilke et al 2001;Farges 2001;Giuli et al 2002Giuli et al , 2003 in order to evaluate the contribution of the different Fe oxidation states and coordination numbers in our samples.…”

Section: Resultsmentioning

confidence: 99%

“…Comparison with spectral data from model compounds with known structure allows estimating the relative percentages of divalent and trivalent iron according to the procedure reported in the literature (Wilke et al 1991;Giuli et al 2002Giuli et al , 2003. The oxidation state of the yellow glasses has been found to vary between 75 and 100 mole% trivalent iron.…”

Section: Discussionmentioning

confidence: 99%

“…The threshold energy was taken as the first maximum of the first derivative of the spectra. Pre-edge peak analysis was carried out following the same procedure reported in Wilke et al (2001) and Giuli et al (2002Giuli et al ( , 2003. The pre-edge peak was fitted by a sum of pseudo-Voigt function and the integrated intensities along with centroid energies were compared with those of the model compounds analyzed here and others in the literature (Wilke et al 2001;Farges 2001) in order to extract information on Fe oxidation state and coordination number in the glasses studied.…”

Section: Data Reductionmentioning

confidence: 99%

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Yellow impact glass from the K/T boundary at Beloc (Haiti): XANES determination of the Fe oxidation state and implications for formation conditions

Giuli

Eeckhout

Koeberl

et al. 2008

Meteorit & Planetary Scien

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Yellow impact glass from the K/T boundary at Beloc (Haiti): XANES determination of the Fe oxidation state and implications for formation conditionsAbstract-We determined the iron oxidation state and coordination number in five samples of yellow impact glass from the Cretaceous-Tertiary (K/T) boundary section at Beloc, Haiti, which formed as the result of impact melting during the Chicxulub impact event. The samples were analyzed by Fe K-edge XANES spectroscopy and the results were compared with published data on eight black impact glasses and one high Si-K impact spherule from the same impact layer. The pre-edge peak of our high-resolution XANES spectra displays evident variations indicative of significant changes in the Fe oxidation state, spanning a wide range from about 75 to 100 mole% Fe 3+ . Yellow K/T glasses have significantly higher Fe 3+ /(Fe 2+ + Fe 3+ ) ratios compared to black K/T impact glasses (from 20 to 75 mole% Fe 3+ ) and high Si-K glass (20 mole% Fe 3+ ). In particular, all the pre-edge peak data on these three types of impact glasses plot between two mixing lines joining a point calculated as the mean of a group of tektites studied so far (consisting of [4] Fe 2+ and [5] Fe 2+ ) to [4] Fe 3+ and [5] Fe 3+ , respectively. Thus, the XANES spectra of the yellow K/T glasses can be interpreted as a mixture of [4] Fe 2+ , [5] Fe 2+ , [4] Fe 3+ , and [5] Fe 3+ . Our observations can be explained by a very large range of oxygen fugacity conditions during melt formation. Furthermore, there is a clear positive relationship between the Fe 3+ /(Fe 2+ + Fe 3+ ) ratio and the Ca content of these glasses, suggesting that the Fe oxidation state was influenced by the relative contribution of Ca-sulfate-and Ca-carbonate-bearing sedimentary rocks at the impact site.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Data Reductionmentioning

confidence: 99%

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Yellow impact glass from the K/T boundary at Beloc (Haiti): XANES determination of the Fe oxidation state and implications for formation conditions

Giuli

Eeckhout

Koeberl

et al. 2008

Meteorit & Planetary Scien

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“…Tektites are glasses ejected from their craters over large distances (so called strewn-fields), but their composition reflects the upper crustal layer, where they have been formed [9]. According to Giuli et al [10], tektites were subjected to cooling under low pressure, while impactites were influenced by a gradient temperature and pressure.…”

Section: The Mystery Of the Origin Of Libyan Desert Glassmentioning

confidence: 99%

“…Giuli et al [10] concluded, based on XANES analysis of the Fe oxidation state, that LDG is definitely an impactite, not a tektite. This idea was also supported by Faulques et al [14] who analysed IR and Raman spectra of several natural glasses, proving a strong similarity in structure between LDG, Darwin glass and vitreous silica.…”

Section: The Mystery Of the Origin Of Libyan Desert Glassmentioning

confidence: 99%

Investigation of inclusions trapped inside Libyan desert glass by Raman microscopy

Swaenen¹,

Stefaniak

Frost

et al. 2010

Anal Bioanal Chem

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Several specimens of Libyan Desert Glass (LDG), an enigmatic natural glass fromEgypt, were subjected to investigation by micro-Raman spectroscopy. The spectra of inclusions inside the LDG samples were successfully measured through the layers of glass and the mineral species were identified on this basis. The presence of cristobalite as typical for high-temperature melt products was confirmed, together with co-existing quartz. TiO 2 was determined in two polymorphic species, rutile and anatase. MicroRaman spectroscopy proved also the presence of minerals unusual for high-temperature glasses such as anhydrite and aragonite.

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Viscosity measurements of crystallizing andesite from T ungurahua volcano ( E cuador)

Chevrel

Cimarelli²,

deBiasi

et al. 2015

Geochem. Geophys. Geosyst.

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Viscosity has been determined during isothermal crystallization of an andesite from Tungurahua volcano (Ecuador). Viscosity was continuously recorded using the concentric cylinder method and employing a Pt‐sheathed alumina spindle at 1 bar and from 1400°C to subliquidus temperatures to track rheological changes during crystallization. The disposable spindle was not extracted from the sample but rather left in the sample during quenching thus preserving an undisturbed textural configuration of the crystals. The inspection of products quenched during the crystallization process reveals evidence for heterogeneous crystal nucleation at the spindle and near the crucible wall, as well as crystal alignment in the flow field. At the end of the crystallization, defined when viscosity is constant, plagioclase is homogeneously distributed throughout the crucible (with the single exception of experiment performed at the lowest temperature). In this experiments, the crystallization kinetics appear to be strongly affected by the stirring conditions of the viscosity determinations. A TTT (Time‐Temperature‐Transformation) diagram illustrating the crystallization “nose” for this andesite under stirring conditions and at ambient pressure has been constructed. We further note that at a given crystal content and distribution, the high aspect ratio of the acicular plagioclase yields a shear‐thinning rheology at crystal contents as low as 13 vol %, and that the relative viscosity is higher than predicted from existing viscosity models. These viscosity experiments hold the potential for delivering insights into the relative influences of the cooling path, undercooling, and deformation on crystallization kinetics and resultant crystal morphologies, as well as their impact on magmatic viscosity.

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Iron oxidation state in the Fe‐rich layer and silica matrix of Libyan Desert Glass: A high‐resolution XANES study

Cited by 62 publications

References 17 publications

Yellow impact glass from the K/T boundary at Beloc (Haiti): XANES determination of the Fe oxidation state and implications for formation conditions

Yellow impact glass from the K/T boundary at Beloc (Haiti): XANES determination of the Fe oxidation state and implications for formation conditions

Investigation of inclusions trapped inside Libyan desert glass by Raman microscopy

Viscosity measurements of crystallizing andesite from T ungurahua volcano ( E cuador)

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