[M-IS09] Weathering and conservation of cultural heritage and geosites

[MIS09-P01] Mineralogical and microclimatic control on the salt weathering of Oya stone

*Luigi Germinario^1,2, Chiaki T. Oguchi² (1.University of Padova, Italy, 2.Saitama University, Japan)

Keywords:Tuff, Underground geoheritage, Efflorescences, Sulfates

Oya tuff is one of the most renowned building stones in Japan. It has been used historically in vernacular architecture, construction, rock-cut and relief sculpture, but its extensive exploitation began only in the Edo period (17th century). The extraction has been conducted mostly underground in over 200 quarries in Tochigi prefecture, with few being still active, many others abandoned or transformed into sites of geoheritage and touristic value. This study deals with the salt weathering of Oya stone, one of the most common decay patterns in underground cultural heritage and geosites, following a mineralogical and environmental approach. The experimental outline included field explorations, mineralogical and geochemical analyses of the rock and its efflorescences, a microclimate monitoring, and the chemical analysis of groundwater and rainwater. The efflorescences turn out to be composed of mixed sulfates, including gypsum, mirabilite, and thenardite. Their formation and stability is strictly dependent on the weathering of accessory phases, in particular pyrite and zeolites, reflected on the groundwater composition; and the subterranean microclimate, especially the variations of relative humidity in time and space, controlling the seasonality and principal composition of the salt mixtures and the occurrence of crystallization/dissolution cycles.