Lapis lazuli provenance study by means of micro-PIXE

In this paper we report about the micro-PIXE characterization of lapis lazuli, for a provenance study of this semi-precious stone, used for glyptic as early as 7,000 years ago. The final aim is to find markers permitting to identify the origin of the raw material coming from three quarries in regions of historical importance: Afghanistan, Pamir Mountains and Siberia. This may help to reconstruct trade routes, especially for ancient objects for which written testimonies are scanty or absent at all. Due to the heterogeneity of lapis lazuli we concentrate our attention on single phases instead of the whole stone; in particular we focused on two of the main phases: lazurite, responsible for the blue colour, and diopside, the more frequent accessory mineral. This study was preceded and completed by means of microanalysis with scanning electron microscopy (SEM-EDX) and cold-cathodoluminescence (cold-CL) analysis. Despite the limited number of analyzed samples, results are sufficient to exclude/suggest a few features as provenance markers, partly confirming what has been previously published in literature.