Universitetskaya nab. 7/9, St. Petersburg, 199034 Russia e-mail: brusspb@yandex.ru Received October 7, 2005...rhodonite toward higher oxygen fugacity values. Johannsenite can be formed in these rocks at even higher...possible to assay the conditions under which johannsenite, another widespread Mn silicate, is stable....constants are now available for calcic rhodonite and johannsenite, phase relations in the Ca–Mn–Si–O system can...(Py) Mn7(Si7O21), rhodonite (Rd) CaMn4(Si5O15), johannsenite (Jh) CaMn(Si2O6), calcite (Cc) CaCO3, braunite |