INFLUENCE OF SURFACE TEXTURES, WEATHERING, AND THICKNESS OF BASALTIC ARTIFACTS ON PXRF ANALYSIS: A CASE STUDY OF BANKS PENINSULA BASALTIC ADZES

Non-Destructive Portable X-Ray Fluorescence (pXRF) is becoming a reliable method of determining geochemistry and provenance of basaltic artifacts. This study investigates the effect of polished and broken surface textures on pXRF analysis, in order to find the most representative location on a basalt artifact to perform analysis. We analyzed 10 representative basalt adzes, sourced from Banks Peninsula on the South Island of New Zealand, and two modified (precision cut) archaeological basalt specimens. Samples were photographed, sketched, and measured, and analysis locations were determined and categorized by surface texture before pXRF analysis was performed. Results indicate major element data (Si, Al, Fe, Mg, Ca) forms artificial populations based on surface texture, while trace element data (Sr, Rb, Zr, Nb) does not. These trace element data series allow for geochemical provenance studies. Within all basaltic adze samples, measured silica is higher on polished surfaces than on pitted, rough or broken surfaces. This decrease in silica content indicates a level of alteration or weathering on these surfaces. Overall, we find that the most representative surface of a basaltic artifact for non-destructive pXRF analysis is a polished surface, with data from these surfaces in close correlation with data from fresh cut surfaces, typically the recommended method of sample preparation. PXRF analysis of polished surfaces is the best practice for polished basalt artifacts which cannot be cut.