Variscite source and source analysis: testing assumptions at Pico Centeno (Encinasola, Spain)

• Published in: Journal of archaeological science 2010-12, Vol.37 (12), p.3146-3157
• Main Authors: Odriozola, Carlos P., Linares-Catela, J.A., Hurtado-Pérez, V.
• Format: Article
• Language: English
• Subjects: Chalcolithic; Cooper age; Europe; Excavation and methods; FTIR; Iberia; Laboratory methods; Methodology and general studies; Neolithic and chalcolithic; Other materials; Physical and chemical analysis; Prehistory and protohistory; Provenance; South West Europe; Typology, technology and attribute analysis; Variscite; XRD; μ-XRF
• ISSN: 0305-4403; 1095-9238
• DOI: 10.1016/j.jas.2010.07.016

The analysis of trade and their implications for understanding social interaction is a major research question of prehistoric research in Europe. Variscite is a rare mineral that offers an excellent opportunity to study trade and exchange patterns in prehistoric Europe through proveniencing of source material. In this paper we discuss the exploitation and exchange of variscite at Pico Centeno mining district during the Copper Age. XRF, XRD, and FTIR analyses of the mineral recovered at Pico Centeno mining district during archaeological survey provides a baseline mineral signature for the source and sub-sources, which were then compared to other Iberian sources and to 44 green beads from 8 megalithic tombs from two different regions, in order to test ‘ provenance postulate’ and distribution models. Mineral sampled during survey at Pico Centeno mining district turned out to be pure variscite phases, while extremely varied for the studied green beads: variscite, muscovite, talc or chlorite. On testing ‘ provenance postulate’ we have focused on compositional comparison of Pico Centeno’s variscite with reference from various geological sources of Western Europe. We found that the concentrations of trace elements do not allow us to establish the origin of the beads, as traditionally claimed, due to the strong natural variability on minor and trace elements of the sources. Instead we found after FTIR analysis, that different proportions of phosphate species, which results in P/Al ratios higher than 1, arose during the genesis of the variscite deposits and resulted from the associated pH and nature of the host-rocks, modifying the concentrations of PO 4 3−, H 2PO 4 − and HPO 4 2−. Thus, the P/Al atomic ratio should be an indication of provenance as it is established during mineral genesis. This issue has not been addressed in any of the other studied sources where this ratio seems to be ≈1.