1. Department of Natural History Sciences Hokkaido University Sapporo 060‐0810 Japan
2. Department of Earth and Planetary Sciences Kyoto University Kyoto 606‐8502 Japan
3. Isotope Imaging Laboratory Creative Research Institution Hokkaido University Sapporo 001‐0021 Japan
4. Institute of Meteoritics University of New Mexico Albuquerque New Mexico 87131 USA
5. Institute of Space and Astronautical Science Japan Aerospace Exploration Agency Sagamihara 252‐5210 Japan