Georesources in Cultural Heritage: the Mg/Ca Ratio in Lime as a Marker of Variations in the Exploitation of Lime Stones in the Vercelli Area (Piemonte, Italy) over the Centuries

Archaeological investigations in the rural settlements of the Po Valley in the Piedmont region of Northern Italy, particularly in the Monferrato area, have revealed a wide range of structures dating from the Roman to the Early Medieval periods. This rural architecture is of great heritage value, as it provides insights into the historical development of Piedmont. This paper focuses on the analysis of lime, one of the oldest and most important building materials, used as binder of bed-ding mortars of three archaeological rural buildings sites dating from the Early Roman imperial Period to the Late Antique phases of medieval fortified centers of Piedmont region. A low-cost and efficient diagnostic geochemical-based method based on the characterization of two oxides present in the lime of mortars and in carbonate rocks of the area (MgO and CaO) is presented. Exploited limestone quarries exploited often have a fairly constant chemical composition and therefore a typical geological Mg/Ca ratio. The variation in this ratio is useful for the relative dating of building walls and for identifying of geological formations and quarries possibly used during the different architectural phases. This paper focuses on this second objective: the study of potential supply areas across the ages related to the ancient communication routes.