Application of LA-ICP-MS to Black Stone Objects Used During the Iron Age in Celtic Europe

Abstract

Black stones—“mixed rocks” composed of both an organic and a mineral fraction—were widely used by ancient populations to make ornamental objects. During the Iron Age in Europe, the Celts made rings, bracelets, beads, and carved vessels out of these rocks. The identification of the geological resources used for the production of these objects is essential for evaluating the distance traveled by these raw materials and for reconstructing ancient exchange networks. The archaeological objects are difficult to characterize due to their heterogeneity, and their characterization is not as advanced as that of other stones used by ancient populations. Characterization of geological samples using LA-ICP-MS has created a preliminary reference database of geological materials, which allowed for the analysis of more than 200 objects from different archaeological sites in Europe. It has thus been possible to demonstrate the great heterogeneity of archaeological materials used and to document a shift in raw material usage between the Hallstatt and La Tene periods. Two different acquisition patterns are proposed: in the first, raw material is transported to manufacturing sites which can be located far from the extraction site, while in the second, production occurs directly at the extraction site. These results allow us to present the distribution network of black stones in Europe. This new approach using LA-ICP-MS is a first step for characterizing black stone artifacts in order to give a first estimation of the chemical composition of these stones. Due to its non-destructiveness, as well as its potential for analyzing large objects such as bracelet or vessel fragments, LA-ICP-MS constitutes a useful characterization tool for black stone artifacts.