## 7 Discussion  
The results of the investigation of the reference samples indicated how assemblages and materials can be distinguished from each other through the combined use of petrographic and non-destructive pXRF analysis. Based on the elements used in this analysis, the geochemical signatures of the samples showed more or less pronounced differences between the ceramic assemblages originating from different sites, while the petrographic investigation of the ceramic pastes provided a more detailed contextualization of the geochemical data. Both mineralogical and geochemical data were strongly in agreement with the complex geology of southern Tuscany. The reference samples from Roccastrada mainly consisted of cooking ware where the intentional addition of a temper, represented by abundant quartz with subordinate and variable amounts of clay pellets, rhyolite and volcanic glass, was observed. In the PCA bi-plots, the samples from Roccastrada formed a more dispersed group that was characterized by a good correlation with Rb, where the abundance and the mineralogical composition of the temper played a significant role in the definition of slight discrepancies in the geochemical signature. The geology of the Roccastrada area is characterized by a diffused presence of Miocene marine clays, represented by fine-grained blue clays with quite abundant micro-fauna (_Argille Azzurre_ Formation) and gray clays with intercalated fine-grained sandstones (_Torrente Raquese_ Formation, or _Pycnotonta_ clays). The abundance of refractory materials, such as volcanic rocks (rhyolite and volcanic glass) and highly siliceous rock assemblages, promoted an intense production of refractory ceramic, such as cooking ware and technical ceramic for smelting activities. The rhyolites of Roccastrada mainly consist of glass (53%), quartz (14-15%), K-feldspar 16%, plagioclase (8-9%), biotite (3-6%) and cordierite (2%), with minor apatite and zircon [70]. Rb\({}^{+}\) substitutes frequently for K\({}^{+}\) in K-feldspars, micas and clay minerals, with a natural tendency to concentrate during the weathering of the parent rock due to ion exchange and adsorption mechanisms. In magmatic systems, Rb\({}^{+}\) highly concentrates during late stages and could substitute for K\({}^{+}\) in K-bearing phyllosilicates (such as mica and biotite) and, to a lesser extent, in K-feldspar [86]. During the first weathering stages, the dismantling of biotite and the plagioclase present in rhyolite rocks leads to a depletion in Rb. In the last stages, following the decomposition of K-feldspars and the alteration of zircon, a consequent increase in Rb depletion, together with K and Zr, is documented [70]. Figure 7: Outline of the main features of the Vetricella assemblage investigated in the present study according to the results from the archaeological, geochemical and petrographic analyses: (**a**) pie chart showing the main ceramic functional classes; (**b**) tree charts showing where the Vetricella assemblage is associated with different production areas depending on the mineralogical and geochemical nature of the pastes. The incidence of each ceramic functional class is also reported. As observed for the samples of Roccastrada, the heterogeneous textural and mineralogical features observed for the fragments from Monterotondo Marittimo represented the main reason for higher fluctuations in the chemical composition. Most of the fine- and medium-grained vessels from this group were mainly represented by a good correlation with Ca (together with Sr) and K, while some coarse ware fragments constituted an intermediate cluster that was represented by Rb. The correlation of fine- and medium-grained samples with Ca was in accord with the geology of Monterotondo Marittimo, as it is mainly represented by the diffuse presence of Miocene blue marine clays, together with limestones, marl and polygenic marine conglomerates.