Challenging an old theory – Portable X-ray fluorescence(pXRF) analyses of greenstone adzes in Rogaland, southwestern Norway

Abstract

The first large scale regional provenance analysis of greenstone and diabase adzes in western Norway was undertaken forty years ago. The study identified two social territories, which have been central in Norwegian archaeology ever since. Concerns have later been raised regarding the validity of the results due to the dominance of descriptive macroscopic methods, mostly based on visual examinations, used to identify the different rock types. To evaluate the older study, we have undertaken portable X-Ray Fluorescence Spectroscopy (pXRF) analyses of greenstone adzes distributed in Rogaland County, southwestern Norway. However, there are also challenges pertaining to this type of surfaceconfined analytical technique, such as effects of patination, surface depositions, surface geometry and spectral interferences. Methodological rigorousness and proper documentation are thus vital in order to produce valid data suited for inter- and intra-group comparative lithic provenance studies. Acknowledging the concerns raised, we describe our procedure, including the process of selecting suitable parameters and measures taken regarding the computation and replicability of the measurement results. Our preliminary results suggest that pXRF is indeed a capable non-destructive method for studying the provenance of greenstone adzes. It may also prompt further research into the exploitation of rock, place and identity in the Mesolithic.