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Revisiting the nontronite Moessbauer spectra

Fabien Baron, Sabine Petit, Martin Pentrak, Alain Decarreau and Joseph W. Stucki
Revisiting the nontronite Moessbauer spectra
American Mineralogist (July 2017) 102 (7): 1501-1515

Abstract

The distribution of ferric iron (Fe (super 3+) ) between the octahedral and tetrahedral sheets of smectites is still an active problem due to the difficulty of identifying and quantifying the tetrahedral ferric iron ( (super [4]) Fe (super 3+) ). Mossbauer spectroscopy has often been used to address this problem, with the spectra being fitted by a sum of doublets, but the empirical attribution of each doublet has failed to yield a uniform interpretation of the spectra of natural reference Fe (super 3+) -rich smectites, especially with regard to (super [4]) Fe (super 3+) , because little consensus exists as to the (super [4]) Fe (super 3+) content of natural samples. In an effort to resolve this problem, the current study was undertaken using a series of synthetic nontronites [Si (sub 4-x) (super [4]) Fe (sub x) (super 3+) ] (super [6]) Fe (sub 2) (super 3+) O (sub 10) (OH) (sub 2) Na (sub x) with x ranging from 0.51 to 1.3. Mossbauer spectra were obtained at 298, 77, and 4 K. Statistically acceptable deconvolutions of the Mossbauer spectra at 298 and 77 K were used to develop a model of the distribution of tetrahedral substitutions, taking into account: (1) the (super [4]) Fe (super 3+) content; (2) the three possible tetrahedral cationic environments around (super [6]) Fe (super 3+) , i.e., [4Si]-(3 (super [6]) Fe (super 3+) ), [3Si (super [4]) Fe (super 3+) ]-(3 (super [6]) Fe (super 3+) ), and [2Si 2 (super [4]) Fe (super 3+) ]-(3 (super [6]) Fe (super 3+) ); and (3) the local environment around a (super [4]) Fe (super 3+) , i.e., [3Si]-(2 (super [6]) Fe (super 3+) ) respecting Lowenstein's Rule. This approach allowed the range of Mossbauer parameters for (super [6]) Fe (super 3+) and (super [4]) Fe (super 3+) to be determined and then applied to spectra of natural Fe (super 3+) -rich smectites. Results revealed the necessity of taking into account the distribution of tetrahedral cations ( (super [4]) R (super 3+) ) around (super [6]) Fe (super 3+) cations to deconvolute the Mossbauer spectra, and also highlighted the influence of sample crystallinity on Mossbauer parameters.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 102
Serial Issue: 7
Title: Revisiting the nontronite Moessbauer spectra
Affiliation: Universite de Poitiers, Institut de Chimie des Milieux et Materiaux de Poitiers, Poitiers, France
Pages: 1501-1515
Published: 201707
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 64
Accession Number: 2017-064773
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 9 tables
Secondary Affiliation: University of Illinois at Urbana-Champaign, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201734
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