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Tobelite and NH (sub 4) (super +) -rich muscovite single crystals from Ordovician Armorican sandstones (Brittany, France); structure and crystal chemistry

Ernesto Mesto, Fernando Scordari, Maria Lacalamita and Emanuela Schingaro
Tobelite and NH (sub 4) (super +) -rich muscovite single crystals from Ordovician Armorican sandstones (Brittany, France); structure and crystal chemistry
American Mineralogist (August 2012) 97 (8-9): 1460-1468

Abstract

The crystal structures of tobelite and NH (sub 4) (super +) -rich muscovite from the sedimentary rocks of the Armorican sandstones (Brittany, France) have been solved for the first time by single-crystal X-ray diffraction. The structural study was integrated by electron probe microanalyses, and X-ray photoelectron and micro-Fourier transform infrared spectroscopy. The crystals belong to the 2M (sub 2) polytype with the following unit-cell parameters: a = 9.024(1), b = 5.2055(6), c = 20.825(3) Aa, and beta = 99.995(8) degrees for tobelite and a = 9.027(1), b = 5.1999(5), c = 20.616(3) Aa, and beta = 100.113(8) degrees for NH (sub 4) (super +) -rich muscovite. Structure refinements in the space group C2/c converged at R (sub 1) = 8.01%, wR (sub 2) = 8.84% and R (sub 1) = 5.59%, wR (sub 2) = 5.63% for tobelite and NH (sub 4) (super +) -rich muscovite, respectively. X-ray photoelectron spectroscopy revealed nitrogen environments associated either with inorganic (B.E. 401.31 eV) or organic (B.E. 398.67 eV) compounds. Infrared spectra showed, in the OH (super -) -stretching region (3700-3575 cm (super -1) ), two prominent bands, centered at approximately 3629 and approximately 3646 cm (super -1) , and two shoulders at approximately 3664 and approximately 3615 cm (super -1) that were assigned to Al (super 3+) Al (super 3+) []-OH (super -) arrangements having OH (super -) groups affected by different local configurations. In addition, a series of overlapping bands from about 3500 to 2700 cm (super -1) characteristic of the NH (sub 4) (super +) -stretching vibrations, a main band at approximately 1430 and a shoulder at approximately 1460 cm (super -1) that were associated to the NH (sub 4) (super +) -bending vibration (nu (sub 4) ) were also present. The ammonium concentration was semi-quantitatively estimated in both crystals from the absorbance of the OH (super -) -stretching and NH (sub 4) (super +) -bending vibrations in the infrared spectra. An additional estimate was obtained for the NH (sub 4) (super +) -rich muscovite by considering the normalized peak area between K2p (sub 3) (sub /) (sub 2) and N1s in the X-ray photoelectron spectrum. The obtained values are in agreement with those derived from the interlayer spacing in the simulated X-ray powder diffraction spectra. The results of this integrated approach converged to (K (sub 0.18) Na (sub 0.01) NH (sub 4) (super +) (sub 0.62) ) (sub Sigma =0.81) (Al (sub 1.98) Fe (super 2+) (sub 0.02) ) (sub Sigma =2.00) (Si (sub 3.19) Al (sub 0.81) ) (sub Sigma =4.00) O (sub 10.00) OH (sub 2.00) for tobelite and to (K (sub 0.46) Na (sub 0.03) Ba (sub 0.01) NH (sub 4) (super +) (sub 0.36) ) (sub Sigma =0.86) (Al (sub 1.98) Mg (sub 0.01) Fe (super 2+) (sub 0.01) V (super 3+) (sub 0.01) ) (sub S=2.01) (Si (sub 3.13) Al (sub 0.87) ) (sub Sigma =4.00) O (sub 10.00) F (sub 0.08) OH (sub 1.92) for NH (sub 4) (super +) -rich muscovite.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 97
Serial Issue: 8-9
Title: Tobelite and NH (sub 4) (super +) -rich muscovite single crystals from Ordovician Armorican sandstones (Brittany, France); structure and crystal chemistry
Affiliation: Universita di Bari, Dipartimento di Scienze della Terra e Geoambientali, Bari, Italy
Pages: 1460-1468
Published: 201208
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 52
Accession Number: 2012-079914
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
N46°30'00" - N49°45'00", W04°49'60" - E00°00'00"
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: 201242
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