1. Department of Crystallography, St. Petersburg State University, University Emb. 7/9, 199034 St. Petersburg, Russia, Fax: (+43) 512‐5072926
2. Institut für Mineralogie und Petrographie, Universität Innsbruck, Innrain 52, 6020 Innsbruck, Austria
3. Institute of Physical Chemistry, Russian Academy of Sciences, Leninskiy prospect 31, 119991 Moscow, Russia