gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1998.62A.3.226 A Comparison of Modern Mass Spectrometric Methods for Th Isotope Ratio Measurement Zindler A. National High Magnetic Field Laboratory, and Department of Geosciences, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32306, USA Reid M. W.M. Keck Foundation Center for Isotope Geochemistry, Department of Earth and Space Sciences and IGPP, UCLA, Los Angeles, CA 90095-1567, USA Albarede F. Blichert-Toft J. Laboratoire des Sciences de la Terre, Ecole Normale Superieure de Lyon, 46, Allee d'Italie, 69364 Lyon Cedex 7, France 1998 62A 3 1703 1704 Copyright © 1998, The Mineralogical Society 1998