ESEM-EDS Investigation of the Weathering of a Heritage Sydney Sandstone

The degradation of Sydney sandstone used to build the heritage St Mary's Cathedral in Sydney, Australia, has been investigated using environmental sca nning el ectron microscopy combined with energy dispersive X-ray spectroscopy. This technique provided the structural details of the cementing clay and an elemental characteri zation the sandstone. The observed differences in the elemental composition of the unweathered and weathered sa ndsto nes were asso ciated with changes to the clay microstru ctu re upon weather­ ing. The resu lts support the substitution theory that FeH replaces AP "'" in the kaolinite clay component upon weatherin g. An examination of the impurities present prior to a nonstructural iron removal treatment revealed th e presence of minerals that may provide a source of the elements responsible for the substitution process.