Analytical Diagnosis of a Rare Egyptian Marble Minbar: Mineralogical Composition and Salt Weathering

This study presents a historical, archaeological, and scientific investigation of a rare marble minbar dated to 1905 CE (1323 AH) in Al-Omari Mosque, Demira Village, Dakahlia Governorate, Egypt. The minbar was examined using portable digital microscopy, polarized light microscopy (PLM), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX), and X-ray diffraction (XRD). The analysis confirms that the stone is predominantly calcite and that its deterioration is driven mainly by salt weathering. Two types of salts, halite and gypsum, were identified, resulting in phenomena such as peeling, pitting, whitish stains, surface erosion, and material loss. Microscopic and SEM observations reveal salt crystallization, surface roughening, microcracks, and structural weakening of the marble. The decay is attributed primarily to past cleaning practices by the local community, who repeatedly washed the minbar with tap water before the mosque was formally registered as an archaeological monument, and secondarily to groundwater-induced rising damp within the minbar and other stone elements in the mosque. These moisture sources favored the crystallization of salts, compounded by diurnal and seasonal temperature fluctuation which govern the rate of evaporation of saline solutions and their subsequent recrystallization, in addition to the expansion and contraction processes of the minerals present in the marble of the minbar. The findings underscore the critical role of salts in the deterioration of early twentieth-century marble heritage in Egypt and provide a scientific basis for future conservation strategies.