Abstract
Crystal-structural changes accompanied by oxidation and dehydrogenation processes have been examined for holmquistite, sodic-calcic and sodic amphiboles in which all Fe2+ ions occur at the M1 and M3 sites, using infrared and Mössbauer spectroscopy. When almost all Fe2+ are oxidized to Fe3+, a new OH-stretching band E appears at lower frequency (∼ a few cm−1) than the principal C band. This band is assigned to (MgMgFe3+)–OH stretching and its configuration to O2−–(MgMgFe3+)–(OH)−. The occupancy of Fe3+ at M1 increases greatly by oxidation and dehydrogenation.
