1. Comenius University, Faculty of Natural Sciences, Department of Mineralogy, Petrology and Economic Geology, Ilkovičova 6, 841 04, Bratislava, Slovakia
2. University of Oulu, Faculty of Technology, Fiber and Particle Engineering Research Unit, Pentti Kaiteran katu 1, 90 014 Oulu, Finland
3. University of Bern, Institute of Geological Sciences, Baltzerstrasse 1+3, CH-3012 Bern, Switzerland