Thermal analysis has been employed in a study of the degradation of heritage Sydney sandstone used in St Mary’s Cathedral
in Sydney, Australia. TG and DSC have been used to characterise the clay components removed from weathered and unweathered
sandstone. Two types of kaolin clays — kaolinite and its polymorph, dickite — have been identified. A higher amount of dickite
present in the clay of weathered sandstone indicates that a kaolinite-to-dickite transformation occurs upon weathering. XRD
hot stage analysis was also used to demonstrate the presence of a more thermally stable polymorph of the kaolinite.