The Heritage Value of Karst Rudist Limestones: Aurisina/Nabrežina Stone, Lipica Stone, and Repen Stone of Italy and Slovenia

The Classical Karst Region (Kras-Carso) is a cross-border area between Italy and Slovenia, from which the scientific term “karst” originates. The geodiversity of this region is linked to the evolution of the former Adriatic Carbonate Platform. On this platform, Upper Cretaceous, rudist-rich shallow-marine limestones were deposited, which include the Italian Aurisina limestone (stratigraphic unit) and the Slovenian Repen, Sežana and Lipica formations. These limestone formations are at present commercially exploited as dimension stones on both sides of the border. More significantly, they have played a central role in the cultural heritage of the Karst region, where several historical quarries are still preserved and quarrying is still active. Thanks to their geotechnical and ornamental attributes, they have been used from Roman times to the present in construction and architectural decoration. Their use is documented in several UNESCO World Heritage Sites, including the Roman city of Aquileia (Udine), the Mausoleum of Theodoric in Ravenna, and the historic centres of Vienna and Budapest. This paper examines the petrographical and geotechnical properties of the varieties of the different Karst rudist limestones, along with their quarrying history and their long-standing architectural use, to assess their heritage value for nomination as Global Heritage Stone Resource. While all types of Karst rudist limestones are similar for their aesthetic and technical value, the Aurisina/Nabrežina Stone stands apart because of its historical value and is therefore the most promising candidate to be nominated as Heritage Stone.