New markers to identify the provenance of lapis lazuli: trace elements in pyrite by means of micro-PIXE
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Lapis lazuli has been used for glyptics and carving since the fifth millennium BC to produce jewels, amulets, seals, inlays, etc; the identification of the origin of the stone used for carving artworks may be valuable for reconstructing old trade routes. Since ancient lapis lazuli art objects are precious, only non-destructive techniques can be used to identify their provenance, and ion beam analysis (IBA) techniques allow us to characterise this stone in a fully non-invasive way. In addition, by using an ion microprobe, we have been able to focus the analysis on single crystals, as their typical dimensions may range from a few microns to hundreds of microns.
Provenance markers, identified in previous IBA studies and already presented elsewhere, were based on the presence/absence of mineral phases, on the presence/quantity of trace elements inside a phase and on characteristic features of the luminescence spectra. In this work, a systematic study on pyrite crystals, a common accessory mineral in lapis lazuli, was carried out, following a multi-technique approach: optical microscopy and SEM-EDX to select crystals for successive trace element micro-PIXE measurements at two Italian facilities, the INFN Laboratori Nazionali di Legnaro and the INFN LABEC laboratory in Firenze. The results of this work allowed us to obtain new markers for lapis lazuli provenance identification.
This work was carried out in the framework of the INFN experiment ‘FARE’ and supported by the TEMART project of Regione Toscana. Thanks are due to Prof. Sara Ferri (President of the Accademia dei Fisiocritici) and to Dr. Ferruccio Farsi who kindly provided some of the analysed specimens. The authors are indebted to Ing. Leonardo La Torre for his skilful assistance in microbeam operation at the INFN Laboratori Nazionali di Legnaro.
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