Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (9) Citing Articles via Google Scholar Google Scholar Articles by MELLINI, M. Articles by LINARÈS, J. Search for Related Content GeoRef GeoRef Citation

Insights into the antigorite structure from Mössbauer and FTIR spectroscopies

¹ Dipartimento di Scienze della Terra, Università di Siena, Via Laterina 8, I–53100 Siena, Italy
² Laboratoire de Minéralogie-Cristallographie de Paris, UMR 7590 du CNRS, case 115, Université Pierre et Marie Curie, 4 Place Jussieu, F-75252 Paris Cedex 05, France
³ Laboratoire de Magnétisme et d'Optique, Université de Versailles-Saint Quentin, Avenue des Etats Unis, F-78000 Versailles, France

^* e-mail: vitic{at}unisi.it

Pure, selected samples of antigorite (#7 and #18, from Elba Island veins, Italy, with superperiodicities of 38 and 49 Å, respectively) have been analyzed by Mössbauer and infrared spectroscopies. Mössbauer data indicate that most of the iron is present as ferrous iron (88.6 % Fe²⁺ in #7 and 83.2 % Fe²⁺ in #18). Both ferrous and ferric iron occur in octahedral coordination; ferric iron in tetrahedral coordination has not been detected. The infrared spectra of antigorites #7 and #18 are similar, with minor shifts in peak positions. More in general, the comparison with other vein antigorites from the Elba suite (#2, #4, #11, #16) rules out any relation between modulation wavelength and IR behaviour. Evident differences arise from the comparison between antigorite and lizardite spectra. The absorption bands corresponding to stretching of the basal Si-O bonds are systematically shifted towards higher wavenumbers in antigorite with respect to lizardite (from 951 to 979–991 cm^-1), suggesting higher energy of the bridging bonds. In contrast, antigorite and lizardite show the same IR patterns in the apical Si-O stretching vibrations (1073–1084 cm^-1). The OH stretching region (3700–3400 cm^-1) indicates similar structural arrangement for the inner O-H in antigorite and lizardite, whereas the absence of the broad band at 3440 cm^-1 in antigorite indicates the lack of important hydrogen bonding in the interlayer. Other IR differences (e.g., absence of Si-O bending and of external OH bending in lizardite) are explained as due to different symmetries (monoclinic antigorite vs. trigonal lizardite).

We conclude that antigorite and lizardite share common features (similar iron coordination and disordered distribution within the magnesium octahedra), but differ in the oxidation state (more reduced antigorite), in the tetrahedral sheet size (basal Si-O bond shrinked by 0.009 Å in antigorite) and in the interlayer connections mechanism (absence of hydrogen bond in antigorite).

Key-words: antigorite, structure, Elba, Mössbauer, infrared.

This article has been cited by other articles:

				F. FRANCO, L. A. PEREZ-MAQUEDA, V. RAMIREZ-VALLE, and J. L. PEREZ-RODRIGUEZ Spectroscopic study of the dehydroxylation process of a sonicated antigorite European Journal of Mineralogy, April 1, 2006; 18(2): 257 - 264. [Abstract] [Full Text] [PDF]

				G. Capitani, G. Capitani, and M. Mellini The modulated crystal structure of antigorite: The m = 17 polysome American Mineralogist, January 1, 2004; 89(1): 147 - 158. [Abstract] [Full Text] [PDF]