Classification and provenance of soapstones and garnet chlorite schist artifacts from Medieval sites of Tuscany (Central Italy): insights into the Tyrrhenian and Adriatic trade

Abstract

Soapstones (talc-bearing schists) and garnet chlorite schist artifacts found in Medieval archaeological sites of Tuscany (Central Italy) were classified, in order to define provenance of the different lithotypes. In Italy and throughout the Central Europe, these greenschist facies metamorphic rocks are generally known, among the archaeologists, as the pietra ollare from the Alps. The investigated Tuscan archaeological sites are between 6 and 13th century AD and were strictly linked, in that period, to the well defined network trade running along Tyrrhenian coast. Samples come from little containers used for cooking and preserving food and showing traces of lathe manufacturing at their sidewalls. According to modal mineralogy, petrographic texture, XRD, SEM-EDS and whole rock chemistry we recognised, among the 18 studied findings, three different petrographic groups of the Alpine pietra ollare. (i) Fine grained magnesite talc schists (i.e. soapstones) from outcrops of the Central Alps located in the Valchiavenna area. (ii) Garnet chlorite schists from the Valle d'Aosta region. (iii) Amphibole talc schists (i.e. soapstones) with a provenance in the Ticino area. It is worth noting that artifacts of pietra ollare lithotypes from the Western Alps (i.e. garnet chlorite schists and amphibole talc schists) were not detected in the archaeological sites of the Middle Adriatic coast of the Central Italy, belonging to the same Medieval time interval. This emphasises that the petrographic groups of pietra ollare from the Alps spread to the south of the Po Plain according to Western and Eastern trade along the Italian Peninsula, using respectively, the Tyrrhenian and the Adriatic Sea commercial routes.