Matera building stones: Chemical, mineralogical and petrophysical characterization of the calcarenite di gravina formation.

Matera (Basilicata, southern Italy) was awarded the World Heritage Site status by the UNESCO since 1993, and has been named the European Capital of Culture in 2019. It is one of the most ancient towns in the world, whose historical centre was totally built by a weakly lithified and highly porous lower Pleistocene sedimentary building stone, known as Gravina Calcarenite. This easily workable rock was quarried since prehistoric times, and it was used for building different kinds of constructions from the rupestrian settlement to gorgeous historic palaces during the XVIII century. Calcarenite, however, can be an extremely heterogeneous building material depending on the composition of the particles and their characteristics. After a geological survey, it was possible to recognize two main varieties of this building stone, which were in turn subdivided into six lithofacies (corresponding to sub-typologies of building stones). As a first approach, we have characterized, in terms of building stone quality, six lithofacies: basal bioclastic calcarenite, calcirudite-microconglomerate lithofacies, lithoclastic calcarenite, large bivalve bioclastic calcarenite, rhodolith bioclastic calcarenite, and fine bioclastic calcarenite. We focused on the three typologies that were mainly used as building stone (lithoclastic calcarenite, large bivalve bioclastic calcarenite, and fine bioclastic calcarenite). Mineralogical, petrographical and petrophysical analyses have been carried out according to European standard rules to highlight the main characteristics of the different calcarenite types when used as building stones. These three lithofacies show different petrophysical behavior indicating that large bivalve calcarenite and lithoclastic calcarenite lithofacies have slightly different but characteristic mechanical properties related to the primary influence of grain composition, early cementation and micrite contents. Moreover, fine bioclastic calcarenite lithofacies results to be the worst building stone because it is intensely heterogeneous in porosity, cementation and general petrophysical features because of its intense bioturbation. © 2019 International Conference on Metrology for Archaeology and Cultural Heritage.