Appearance of infrared (MgMgFe~(3+))-OH stretching band in heat- treated holmquistites, sodic-calcic and sodic amphiboles

摘要

Crystal-structural changes accompanied by oxidation and dehydrogenation processes have been examined for holmquistite, sodic-calcic and sodic amphiboles in which all Fe~(2+) ions occur at the M1 and M3 sites, using infrared and Mbssbauer spectroscopy. When almost all Fe~(2+) are oxidized to Fe~(3+), a new OH-stretching band E appears at lower frequency (～ a few cm~(-1)) than the principal C band. This band is assigned to (MgMgFe~(3+))-OH stretching and its configuration to O~(2-)-(MgMgFe~(3+))-(OH)~-. The occupancy of Fe~(3+) at M1 increases greatly by oxidation and dehydrogenation.