Gypsum formation in non-calcareous building sandstone: A case study of Scrabo sandstone

This paper addresses one central issue of building stone research: An origin for calcium in gypsum formation in non-calcareous sandstones. A comparative study of Scrabo sandstone from outcrops and a 120-year-old building in central Belfast shows how weathering has significantly altered the mineralogy. Preliminary results suggest that the occurrence of gypsum throughout the stone blocks is related to chemical reactions between a pore-filling mineral constituent, actinolite (Ca Mg amphibole), and sulphur oxides from urban pollution. These findings advocate an internal source of calcium for gypsum formation, and provide new evidence to explain the enhanced decay displayed in some Scrabo sandstone.