1. Mineralogy Department, Institute for Geosciences, Friedrich‐Schiller University, Carl‐Zeiss‐Promenade 10, Jena, Germany, Fax: +49‐3641‐948702, http://www.geo.uni‐jena.de
2. Institute of Mineralogy and Crystallography, University of Vienna, Geocentre, Althanstr. 14, 1090 Vienna, Austria, http://www.univie.ac.at/Mineralogie/