Bone or shell? Using ED-XRF to determine the nature of prehistoric ornaments

When determining the nature of prehistoric ornaments, the degree of transformation can play an important role, as occasionally the technical traces (as polishing or smoorthing) applied to define the morphology of the desired object can substantially modify the original surface. When this occurs, it is sometimes difficult to determine the nature of the object. In this paper a protocol to quickly and easily distinguish between shell and bone materials in a non-destructive manner is presented. Both elements were frequently used during prehistory to make personal ornaments. After a first analysis with a stereoscopic microscope and a basic morphological description to observe the degree of standardization of the selected objects, energy dispersive X-ray fluorescence (ED-XRF) was applied to determine chemical components. To test the validity of this protocol, the study focused on the analysis of discoidal beads and V-perforated buttons whose nature, in some cases, had already been noted using macroscopic methods. Prehistoric ornaments analysed were recovered at three archaeological sites of NE Iberia: Tutes de Menús Cave (Béixec, Montellà i Martinet, Lleida, Spain), Espluga Negra Cave (Vilanova de Meià, Lleida, Spain) and Ànimes Cave (Matadepera, Barcelona, Spain).