The Pietra Ollare of the medieval archaeological site of Monte Giove (Fano, Marche Region, Central Italy) unveils further constraints for the Alpine Valchiavenna soapstone trade

Abstract

More than two hundred fragments of pietra ollare were discovered in the Monte Giove Medieval archaeological site as erratic pieces on the surface and within some of the 120 silos of underground pits for food storage, dated between the 9th and 11th centuries AD. Twelve representative samples were selected for thin section petrography, X-ray powder diffraction and whole rock major-trace element composition. The entire data provide a homogeneous petrographic classification for the stone findings: carbonate (magnesite) talc schists, also known as soapstones. Among the Alpine pietra ollare lithotype groups (Mannoni et al. 1987), these samples belong to the fine-grained and grey to light-green coloured soapstones, namely the “petrographic group D”, whose quarrying sites in antiquity were commonly recognised in the Valchiavenna area (Central Alps). This pietra ollare provenance of Monte Giove thus reinforces the so-called “Valchiavenna soapstone trade”, from the Mera-Adda-Po Rivers towards the Adriatic harbour of Comacchio, where several pietra ollare findings, dating back between the 7th and 9th centuries, are also well documented. The role played by Comacchio as a Medieval commercial hub for pietra ollare is also discussed in the framework of Monte Giove findings.