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A multi-method characterization of natural terrestrial birnessites

Florence T. Ling, Jeffrey E. Post, Peter J. Heaney, Cara M. Santelli, Eugene S. Ilton, William D. Burgos and Arthur W. Rose
A multi-method characterization of natural terrestrial birnessites
American Mineralogist (June 2020) 105 (6): 833-847

Abstract

With a focus on a large set of natural birnessites collected from terrestrial, freshwater systems, we applied and compared the capabilities of X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) to characterize crystal structure and chemistry. Using XRD, we successfully identified 3 of the 11 natural birnessite samples as hexagonal rancieite-like phases, but the remaining samples yielded less interpretable "3-line" diffraction patterns with broad, asymmetrical peaks at d-spacings of approximately 7.2, approximately 2.4, and approximately 1.4 Aa. EXAFS analysis suggested that many of these samples had characteristics of both triclinic and hexagonal birnessite. However, application of EXAFS to the rancieite-like phases yielded unreasonably high concentrations of triclinic birnessite as an intergrowth, calling into question the use of synthetic hexagonal H-birnessite as an appropriate standard in the linear combination fitting of EXAFS data for natural birnessites. FTIR spectroscopy of the "3-line" birnessite samples successfully distinguished triclinic and hexagonal constituents, and analyses of peak positions suggested that natural birnessites occur as a full spectrum of triclinic and hexagonal intergrowths. XPS analysis of these samples revealed that higher Mn (super 3+) concentrations relative to Mn (super 2+) and Mn (super 4+) are correlated to increased proportions of triclinic birnessite.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 105
Serial Issue: 6
Title: A multi-method characterization of natural terrestrial birnessites
Affiliation: Pennsylvania State University, Department of Geosciences, University Park, PA, United States
Pages: 833-847
Published: 202006
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 80
Accession Number: 2020-049549
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
Secondary Affiliation: Smithsonian Institute, Department of Mineral Sciences, USA, United StatesUniversity of Minnesota, USA, United StatesPacific Northwest National Laboratory, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202014
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