Thermal behavior of chlorites of the clinochlore-chamosite solid solution series: Oxidation of structural iron, hydrogen release and dehydroxylation

The thermal reactions of natural trioctahedral chlorites of the clinochlore-chamosite solid solution series were studied by simultaneous thermal analysis supplemented by comprehensive mineralogical analysis. The Fe(II) and Fe(III) amount varied between 0.09 and 4.15 p.f.u. and 0.06 and 0.22 p.f.u., respectively. Content and distribution of Fe(II) determined strongly the thermal behavior. The oxidation of Fe(II) to Fe(III) took place prior or occurred in parallel to the dehydroxylation (DHX) of the interlayer octahedral sheet (IOS). During the oxidation, one electron is transferred to the proton of the octahedral hydroxyl groups forming either H2 in N2 atmosphere or reacting further to H2O in synthetic air (SynA). Thereby, the ratio of mass loss of both DHX of IOS and the 2:1 layers varied in dependency of the Fe(II) position. At high Fe content in chlorites and bulk materials, ferromagnetic phases occurred after heating under N2.