Field-Portable Non-Destructive Analysis of Lithic Archaeological Samples by X-Ray Fluorescence Instrumentation using a Mercury Iodide Detector: Comparison with Wavelength-Dispersive XRF and a Case Study in British Stone Axe Provenancing

Abstract

Field-portable X-ray fluorescence (PXRF) instrumentation incorporating three radioisotope sources and a mercury (II) iodide detector has been evaluated in the non-destructive quantitative chemical analysis of lithic artefacts of archaeological interest. The method was tested by comparing PXRF analyses of 19 archaeological samples of fine- to medium-grained igneous rocks with laboratory wavelength-dispersive whole-rock XRF analyses of the same samples. Elements determined were K, Ca, Ti, Mn, Fe, Rb, Sr, Y, Zr, Nb, Ba, Cu, Zn and Pb, with detection limits for the most sensitively-determined elements of 6–14ppm. PXRF analyses on fresh rock or artefact surfaces compare very well with the bulk WDXRF determinations, but weathered surfaces can give results significantly different from the corresponding bulk composition, especially for K, Ca, Ti and Fe. Seven British prehistoric stone implements (axes, axe-hammers and a mace-head) in the National Museum and Gallery, Cardiff, were analysed non-destructively by PXRF to assess the potential of this method in the provenancing of stone implements. Of four implements which had previously been assigned on petrographic grounds to Implement Petrology Committee (IPC) Group XIII (Preseli dolerite), two were confirmed as Group XIII and two have chemistry (and mineralogy) unlike Group XIII dolerite. Two implements previously assigned to IPC Group VIII (a rhyolite Group with suggested sources mainly in south Wales) have chemical characteristics which suggest sources respectively at an axe-manufacturing site near Carnalw in south-west Wales, and on the far west or north Pembrokeshire coast. The final implement, an axe, could not be assigned to any source with certainty either on petrographic or chemical grounds.