1. Institute for Rock Magnetism, Department of Earth Sciences, University of Minnesota, 116 Church Street SE, Minneapolis, Minnesota 55455, U.S.A.
2. Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, U.S.A.
3. Chemistry Department, McGill University, 801 Sherbrooke St. W, Montréal, Québec H3A 0B8, Canada