A model for the OH defect incorporation in kyanite based on polarised IR spectroscopic investigations

Autor(en)

Anton Beran, Arkadiusz Wieczorek, Eugen Libowitzky

Abstrakt

Kyanite samples from different geological environments contain structural OH defects equivalent to about 0.0003-0.0058 wt.% H2O. Two main types of IR spectra can be discerned in the region of the OH stretching vibration. One spectral type contains bands at 3386, 3410 and 3440 cm-1 with approximately equal intensities. The second, most common type of kyanite spectra is characterised by a dominating band at 3386 cm-1 and only weak bands at 3410 and 3440 cm-1. Clearly separated band maxima occur at 3275 and 3260 cm-1. Slightly turbid crystal parts reveal additional OH absorption features in the 3600 cm-1 region which can be assigned to OH groups of layer silicates, occurring as submicroscopic mineral inclusions. From the thermal treatment of kyanite samples up to 1000 °C it is evident that in course of heating processes the included hydrous mineral phases act as hydrogen source for the formation of OH defects inherent to the kyanite structure. The pleochroic scheme of the 3386 cm-1 band, determined on two oriented crystal sections, indicates a preferred orientation of the OH dipole in the n'β direction of the (100) cleavage plane. This orientation is in coincidence with an incorporation model where OB acts as donor oxygen of an OH group pointing directly to the centrosymmetric OB, atom. The pleochroic behaviour of the 3440 cm-1 band suggests the replacement of OM oxygen atoms by OH defects roughly pointing to OC and the pleochroism of the 3410 cm-1 band corresponds to a model where OC acts as donor oxygen of an OH defect roughly pointing to OM. The pleochroic behaviour of the doublet band at 3275 and 3260 cm-1 is in agreement with an OH group where OF acts as donor and OA as acceptor oxygen. © 2004 Schweiz. Mineral. Petrogr. Ges

Organisation(en)

Institut für Mineralogie und Kristallographie

Journal

Schweizerische Mineralogische und Petrographische Mitteilungen: eine europäische Zeitschrift für Mineralogie, Geochemie und Petrographie

Band

84

Seiten

333-343

Anzahl der Seiten

11

ISSN

0036-7699

Publikationsdatum

2006

Peer-reviewed

Ja

ÖFOS 2012

105113 Kristallographie, 1030 Physik, Astronomie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/f81e4c4a-0808-4a49-9a00-e005e050ce6b