Al-free di-trioctahedral substitution in chlorite and a ferri-sudoite end-member

Abstract

AbstractA compilation of Fe3+-bearing chlorite analyses is used: (1) to investigate the Alfree di-trioctahedral (AFDT) substitution 2Fe3++□= 3(Mg,Fe2+) in chlorite; and (2) to estimate the composition of a ferri-sudoite end-member (Si3Al)[(Fe2+,Mg)2□Al]O10(OH)8within the chlorite solid-solution domain. According to our observations, up to two Fe3+cations might be allocated in the M2-M3 chlorite sites by the substitution AFDT, which does not involve Al. These unexpected observations were made possible by the development of μXANES techniques allowingin situmeasurements ofXFe3+(Fe3+/(Fe2++ Fe3+)) in heterogeneous chlorite. Although further studies are required to confirm the crystallographic position of Fe3+ and refine its ionic/ magnetic behaviour in chlorite, this development creates opportunities for developing new geothermometers.