Fe-57 Mossbauer effect study of bannisterite: a modulated 2 : 1-type phyllosilicate

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Fe-57 Mossbauer effect study of bannisterite: a modulated 2 : 1-type phyllosilicate. / Ferrow, Embaie.

In: Mineralogical Magazine, Vol. 70, No. 2, 2006, p. 187-199.

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TY - JOUR

T1 - Fe-57 Mossbauer effect study of bannisterite: a modulated 2 : 1-type phyllosilicate

AU - Ferrow, Embaie

PY - 2006

Y1 - 2006

N2 - Bannisterite is a modulated 2:1-type phyllosilicate having ten octahedral sites with hydroxyl groups in trans, cis and combined trans-cis configurations. Each octahedral site, depending on its proximity to the layer modulation, is exposed to a different degree of distortion. The electric field gradient at the Fe site and the site distortion are used to propose a model for the site assignment and oxidation mechanism in bannisterite. The results show that two models are compatible with the experimental results of fitting the spectrum of bannisterite. However, the model which allows for site distortion accounts better for the observed line overlap of the Fe-[6](2+) sites. Accordingly, the octahedral sites with a greater degree of distortion are assigned to the Fe-[6](2+) with lower electric quadrupole splitting, and the octahedral sites with lower site distortion are assigned to the Fe-[6](2+) with higher electric quadrupole splitting. Moreover, the ease of oxidation decreases in the order trans > trans-cis > cis.

AB - Bannisterite is a modulated 2:1-type phyllosilicate having ten octahedral sites with hydroxyl groups in trans, cis and combined trans-cis configurations. Each octahedral site, depending on its proximity to the layer modulation, is exposed to a different degree of distortion. The electric field gradient at the Fe site and the site distortion are used to propose a model for the site assignment and oxidation mechanism in bannisterite. The results show that two models are compatible with the experimental results of fitting the spectrum of bannisterite. However, the model which allows for site distortion accounts better for the observed line overlap of the Fe-[6](2+) sites. Accordingly, the octahedral sites with a greater degree of distortion are assigned to the Fe-[6](2+) with lower electric quadrupole splitting, and the octahedral sites with lower site distortion are assigned to the Fe-[6](2+) with higher electric quadrupole splitting. Moreover, the ease of oxidation decreases in the order trans > trans-cis > cis.

KW - electric field gradient

KW - distortion

KW - bannisterite

KW - Mossbauer

KW - assignment

KW - site

U2 - 10.1180/0026461067020323

DO - 10.1180/0026461067020323

M3 - Article

VL - 70

SP - 187

EP - 199

JO - Mineralogical Magazine

JF - Mineralogical Magazine

SN - 0026-461X

IS - 2

ER -