1. Institut für Mineralogie Westfälische Wilhelms‐Universität Münster Corrensstrasse 24 D‐48149 Münster Germany
2. Department of Mineralogy and Petrography Natural History Museum Vienna Burgring 7 1010 Vienna Austria
3. Science and Technology Division Corning Incorporated 21 Lynn Morse Rd., Painted Post New York New York 14870 USA