Geological Insights on the Calcareous Tufas (Pietra Spugna) Used as Building and Ornamental Stones in the UNESCO Historical Centre of Urbino (Marche Region, Italy)

A groundbreaking study reclassifies the unique, porous carbonate stone known as 'Pietra Spugna' or 'Tufo spugnoso'—historically used in Roman architecture and later in Urbino’s UNESCO-listed historic center—as calcareous tufas. This classification, supported by physical observations and stable isotope analysis (δ13C and δ18O), sheds new light on the stone's formation process: chemical precipitation of CaCO3 driven by CO2 degassing from calcium-bicarbonate-rich waters, coupled with organic material encrustation in continental environments. Radiocarbon dating reveals these stones formed between 9100 and 4700 years BP, coinciding with the Holocene Atlantic climatic optimum—a period of peak carbonate deposit growth across Mediterranean regions and northern Europe. Ongoing research on a perched springline along the Metauro Valley suggests potential local sources for Roman-exploited blocks, offering insights into the provenance of Urbino’s architectural heritage.

Santi, P., Renzulli, A., Veneri, F., Tonelli, G., Tramontana, M., Taussi, M., Calcagnile, L., & Quarta, G. (2023). Geological Insights on the Calcareous Tufas (Pietra Spugna) Used as Building and Ornamental Stones in the UNESCO Historical Centre of Urbino (Marche Region, Italy). Heritage, 6(5), 4227–4242. https://doi.org/10.3390/heritage6050223