1. Department of Geology Institute of Ecology and Earth Science University of Tartu Ravila 14A Tartu 50411 Estonia
2. Department of Chemistry University of Helsinki P.O. Box 55 (A.I. Virtasen aukio 1) FI‐00014 Finland
3. Institut für Planetologie Westfälische Wilhelms Universität Münster Wilhelm‐Klemm‐Str. 10 Münster 48149 Germany
4. Institute of Chemistry University of Tartu Ravila 14A Tartu 50411 Estonia
5. Geological Survey of Finland Neulamäentie 5 Kuopio FI‐70211 Finland