The origin of Mg sulphate and other salts formed on pure calcium carbonate substrate - Tufa stone blocks built into the Gradac Monastery, Serbia

Epsomite and hexahydrate occur in the form of efflorescence on the church walls made of pure calcium carbonate - tufa stone. A few sources of magnesium are responsible for the precipitation of Mg-salts at the block surfaces: lime mortar with Mg-rich aggregates, repair lime cement mortar, the dolostone of the rubber core, and the monastery basement composed of Mg-rich rocks. Possible sources of sulphate are: repair lime cement mortar and soil solution. The permanent presence of different solution types in the tufa pore system enabled the precipitation of salts in the following order: calcite/dolomite, gypsum, Mg-sulphate phases, syngenite and blodeite. (C) 2015 Elsevier Ltd. All rights reserved.