Al-free di-trioctahedral substitution in chlorite and a ferri-sudoite end-member

Trincal, Vincent; Lanari, Pierre

doi:10.1180/claymin.2016.051.4.09

Cited by 21 publications

(23 citation statements)

References 69 publications

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“…In any case, our results do not support the existence of ditrioctahedral ferric end-members as recently proposed for common chlorites (Vidal et al 2016;Trincal and Lanari 2016)-even if at least one is needed to account for Fe 3+ -rich sudoite (Billault et al 2002). Rather, the high contents of Fe 3+ found in our samples are mostly linked to proton loss, with a potential contribution of Al 3+ -Fe 3+ exchange.…”

Section: Substitutions and Possible Ferric End-members For Chloritecontrasting

confidence: 78%

“…5b). This trend has already been identified by Trincal and Lanari (2016;also Billault et al 2002, in Fe-rich sudoite) and explained by coupled substitution of three divalent cations by two Fe 3+ cations, similarly to the di-trioctahedral substitution: VI o + 2 VI Fe 3+ = 3 VI (Mg,Fe 2+ ). This exchange reaction must be completed by some Al = Fe 3+ substitution, first to account for analyses with Fe 3+ > 2 pfu (Figs.…”

Section: Substitutions and Possible Ferric End-members For Chloritesupporting

confidence: 69%

“…In the octahedral sheet of the 2:1 layer, with a multiplicity of 1 pfu and by analogy with the structure of dioctahedral micas (e.g., muscovite), the M1 site is a more likely target for vacancies than M2, as already proposed by Vidal et al (2001) for their sudoite end-member. The same analysis indicates that for compositions containing proportions of the "pyrophyllitegibbsite" end-member (proposed by Inoue et al 2009, andby Trincal and, with two vacancies, these should be assigned first to M1, then to M4.…”

Section: Incorporation Of Fe 3+mentioning

confidence: 91%

“…A compilation of analyses from the literature was used for comparison, taken from Trincal and Lanari (2016) but screened with more stringent criteria:…”

Section: Methodsmentioning

confidence: 99%

“…Homovalent exchange of Al by Fe 3+ (Al = Fe 3+ ) has been suggested as a possible mechanism both in octahedral (Vidal et al 2005;Inoue et al 2009;Lanari et al 2014) and tetrahedral position to a smaller extent (Lanson et al 2012;Muñoz et al 2013). Trincal and Lanari (2016) highlighted a di-trioctahedral substitution VI o + 2 VI Fe 3+ = 3 VI (Mg,Fe 2+ ) that they modeled with a "di-ferri-sudoite" end-member in which Fe 3+ replaces Mg and Fe 2+ in M2 and M3 sites (see Table 1). Vidal et al (2016) suggested another "ferri-sudoite" end-member, with one Fe 3+ ion in the M4 site per formula unit (Table 1), following the cation distribution of their previous model (Vidal et al 2006).…”

Section: Introductionmentioning

confidence: 99%

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A XANES and EPMA study of Fe3+ in chlorite: Importance of oxychlorite and implications for cation site distribution and thermobarometry

Masci

Dubacq

Verlaguet

et al. 2019

American Mineralogist

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Chlorite is a ubiquitous product of metamorphism, alteration of magmatic rocks and hydrothermal processes owing to its large stability field and wide compositional range. Its composition is governed by several substitutions and has been used as a geothermometer, on the basis of empirical, semi-empirical, and thermodynamic models. As in some other phyllosilicates of petrological interest, the oxidation state of iron in chlorite may differ from the usually assumed divalent state. However, the crystal chemistry of trivalent iron in chlorite remains poorly known, and the thermodynamic properties of ferric chlorite are missing from databases used for petrological modeling. As part of an attempt to fill this gap, we present results from in situ, micrometer-scale measurements of the oxidation state of iron in various chlorite-bearing samples. X-ray absorption near-edge spectroscopy (XANES) was combined with electron probe microanalysis (EPMA) on the same crystals. Results show iron oxidation states varying from ferrous to ferric; iron is in octahedral coordination in all ferromagnesian chlorites but to ~25% tetrahedral in the lithian chlorite cookeite (1.0 wt% Fe 2 O 3(total)). Absolute amounts of ferric iron cover an unprecedented range (0 to ~30 wt% Fe 2 O 3). For highly magnesian, ferric chlorite, Fe concentrations are low and can be accounted for by Al = Fe 3+ substitution. In Fe-rich samples, Fe 3+ may exceed 2 atoms per formula unit (pfu, 18 oxygen basis). When structural formulas are normalized to 28 charges corresponding to the standard O 10 (OH) 8 anionic basis, these measurements define the exchange vector of a di-trioctahedral-type substitution: 3 VI (Mg, Fe 2+) = VI o + 2 VI Fe 3+ , as described in earlier studies. However, structural formulas calculated on the basis of the oxygen contents actually measured by EPMA show that this trend is an artifact, due to the neglect of variations in the number of protons in the structure. Our measurements indicate increasing hydrogen deficiency with increasing Fe 3+ content, up to ~ 2 H + pfu in the Fe 3+-rich chlorite samples, corresponding to a net exchange vector of the type R 2+ + H + = Fe 3+. These results do not support substitutions toward di-trioctahedral ferric endmembers, and highlight the need for considering substitution toward an "oxychlorite" (i.e., H-deficient) ferric component, close to tri-trioctahedral, with an O 12 (OH) 6 anionic basis, even in green, pristine-looking chlorite. The effects of iron oxidation and H deficiency on chlorite geothermometers were explored. They are deterring if H deficiency is ignored but, given the sensitivity of most thermometers to octahedral vacancy, the assumption Fe total = Fe 2+ is still safer than using high measured Fe 3+ contents and the standard 28 charge basis, which artificially increases vacancies. In such ferric chlorites, EPMA measurement of oxygen allows a fair estimate of H content if Fe 3+ /Fe 2+ is known; it should be more systematically implemented. For the same reasons, literature data reporting Fe 3+-ri...

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Section: Substitutions and Possible Ferric End-members For Chloritecontrasting

confidence: 78%

Section: Substitutions and Possible Ferric End-members For Chloritesupporting

confidence: 69%

Section: Incorporation Of Fe 3+mentioning

confidence: 91%

“…A compilation of analyses from the literature was used for comparison, taken from Trincal and Lanari (2016) but screened with more stringent criteria:…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A XANES and EPMA study of Fe3+ in chlorite: Importance of oxychlorite and implications for cation site distribution and thermobarometry

Masci

Dubacq

Verlaguet

et al. 2019

American Mineralogist

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Empirical Raman calibration of trioctahedral ferromagnesium chlorite minerals

Lamm,

Lacroix,

Marshall

et al. 2023

J Raman Spectroscopy

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Chlorite is a common hydrated‐aluminous phyllosilicate mineral group that forms in most geological environments (e.g., hydrothermal, igneous, sedimentary, and metamorphic). The chemical composition of chlorite depends on several factors including temperature, pressure, fluid, and bulk rock composition. Raman spectroscopy is proposed as a quick and cost‐effective alternative to scanning electron microscopy and electron probe micro‐analysis, which involve complex sample preparation. In this paper, we demonstrate that Raman spectroscopy is a viable technique to determine the chemical composition of chlorite. Our results show that chlorite's Raman spectra changes quantitatively as a function of its chemical composition. Iron (Fe) and magnesium (Mg) content (APFU) is linearly correlated with the peak positions of three bands: Band 1 (99–104 cm−1), Band 8 (546–553 cm−1), and Band D (3,570–3,580 cm−1). In contrast, silicon (Si) and tetrahedral aluminum (AlIV) are correlated with a single band's position, Band 9b (663–679 cm−1). We derived 18 empirical rules from these correlations, aiding geoscientists in accurately identifying and determining chlorite composition using Raman spectroscopy. Moreover, this technique holds potential for determining chlorite's chemical composition during planetary exploration, leveraging existing Raman spectrometers deployed on Mars and for future space missions.

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Greenalite-Chamosite composition, geothermometry and oxygen fugacity variations in pisolitic ironstone and carbonates of the Chilpi Group: implication on Paleoproterozoic seawater chemistry

Mohanty,

Mishra

2023

Phys Chem Minerals

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Al-free di-trioctahedral substitution in chlorite and a ferri-sudoite end-member

Abstract: A B S T R AC T : A compilation of Fe3+ -bearing chlorite analyses is used: (1)

Cited by 21 publications

References 69 publications

A XANES and EPMA study of Fe3+ in chlorite: Importance of oxychlorite and implications for cation site distribution and thermobarometry

A XANES and EPMA study of Fe3+ in chlorite: Importance of oxychlorite and implications for cation site distribution and thermobarometry

Empirical Raman calibration of trioctahedral ferromagnesium chlorite minerals

Greenalite-Chamosite composition, geothermometry and oxygen fugacity variations in pisolitic ironstone and carbonates of the Chilpi Group: implication on Paleoproterozoic seawater chemistry

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