The crystal chemistry of birefringent natural uvarovites. Part IV. OH defect incorporation mechanisms in non-cubic garnets derived from polarized IR spectroscopy
- Author(s)
- Michael Andrut, Manfred Wildner, Anton Beran
- Abstract
The anisotropic OH stretching vibrational behavior of three birefringent garnet crystals with compositions close to the uvarovite-grossular binary from the locality Saranov (Ural Mountains, Russia) are investigated in detail by polarized IR microspectroscopy. These garnet samples exhibit low but significantly different water contents (Sar-899 <Sar-w2 <Sar-k12 <0.5 wt.% H2O). The IR polarization behavior in the OH stretching vibrational region of samples Sar-899, Sar-k12, and Sar-w2 complies with orthorhombic, monoclinic, and triclinic crystal symmetry, respectively. The corresponding spectra consist of 14 discernible, partly superimposing absorption bands between 3680 and 3470 cm-1, which are assigned to structurally incorporated hydroxyl groups. According to the individual pleochroic behavior of ten clearly non-isotropic bands, six different pleochroic patterns, i.e. four band doublets and two single bands are distinguished. For the band doublets at 3559/3540 cm-1, 3572/3565 cm-1, and 3595/3588 cm-1, as well as for the single 3618 cm-1 band, models for a structural OH incorporation based on the classical (O4H4) hydrogarnet substitution are proposed. In contrast, for the band doublet at 3652/3602 cm-1 and the single band at 3640 cm-1, OH defect incorporation is explained assuming the presence of vacancies on octahedral or dodecahedral cation positions, leading to [SiO3(OH)] tetrahedral groups. It is concluded that in garnets with low water contents the [SiO3(OH)] substitution plays an essential role as OH defect incorporation mechanism.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- University of Vienna
- Journal
- European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences
- Volume
- 14
- Pages
- 1019-1026
- No. of pages
- 8
- ISSN
- 0935-1221
- DOI
- https://doi.org/10.1127/0935-1221/2002/0014-1019
- Publication date
- 2002
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 1051 Geology, Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/5ec1d68c-dc8d-4389-80d8-23d8cf4b2573