Dear Shao-Yong, you can dissolve the pyrite/chalcopyrite fraction by using the Cr(II) reduction method (see for instance Canfield et al., 1986). Anhydrite is not touched by this procedure. you can dissolve it from separate batches. Good Luck Michael ******************************************************** Dr. Michael E. Boettcher Biogeochemie Max-Planck Institut fuer Marine Mikrobiologie Celsiusstr.1 D-28359 Bremen FRG Tel: 0421-2028-632