Abstract
Volcanic tuffs have a historical tradition of usage in Northern Hungary as dimension stones for monumental construction, Ottoman architecture, common dwellings, etc., admirable at its best in the medieval castles of Eger and Sirok. This research explores tuff deterioration in the castle walls, dealing with the mineralogical composition, microstructure, trace-element geochemistry, and microporosity of the surface weathering products and the near-surface stone substrate. The classic microscopic and mineralogical techniques–optical microscopy, SEM-EDS, and XRD–were supported by ICP-MS and nitrogen adsorption analyses. The textures and mineral assemblages of the tuffs are partly diverse, and so are the weathering characteristics, although including common features such as secondary crystallization of gypsum, swelling clay minerals, and iron oxides-hydroxides; deposition of airborne pollutants, i.e., carbon particles and heavy metals; formation of crusts and patinas; decreased surface microporosity. Nonetheless, the entity of deterioration varies, in relation to air pollution–involving changing emissions from road and rail transport–and the specific tuff texture, porosity, and durability–affecting pollutant absorption. The studied stone monuments offer the possibility to examine materials with analogue composition and petrogenesis but utilized in different environmental contexts, which allow pointing out the environmental and lithological constraints and cause-effect relationships related to surface weathering.
Highlights
The exploitation and usage of volcanic tuffs as dimension stones in Hungary represent part of a quarrying tradition having a great historical significance, commenced as early as the Roman imperial rule in the 1st century BCE
The stone materials used for building and restoring the medieval castles of Eger and Sirok are acid tuffs featuring diverse textures and mineral assemblages, which allow for the recognition of the local quarry sources
The decreased microporosity measured on the stone surface enhances the chemical and technical differences with the host rock and the tuff vulnerability
Summary
The exploitation and usage of volcanic tuffs as dimension stones in Hungary represent part of a quarrying tradition having a great historical significance, commenced as early as the Roman imperial rule in the 1st century BCE. Jeopardizing the preservation of monuments and artworks Their durability can be inferred from relevant petrophysical and mechanical properties [6,7,8,9,10,11], only one study has documented the weathering of the monumental stone: the most recurring decay patterns, i.e., differential erosion, crust formation, crumbling, and other detachment morphologies, are dependent on mineralogy, pore-size distribution, and proportions of matrix, lithics, and pumice [7]. This research will tackle the theme of tuff exploring the mineralogical composition, analogue composition and petrogenesis but deterioration, utilized in different environmental contexts In this microstructure, trace-element geochemistry, and microporosity of the surface weathering products regard, the lithological and environmental constraints and cause-effect relationships relatedand to the near-surface stone in historical monuments. Complementary calculations of mean pore diameter and pore-size distribution by the BJH method (Barrett–Joyner–Halenda) were done, and porosity was estimated from skeletal density [11]
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