Journal Article

Micro-computed tomography and laser micro-ablation on altered pyrite in lapis lazuli to enhance provenance investigation: a new methodology and its application to archaeological cases

Herrmann, Georgina, Aprà, Pietro, Re, Alessandro, Tansella, Francesca, Pichon, Laurent, Moignard, Brice, Picollo, Federico, Lemasson, Quentin, Lo Giudice, Alessandro, Magalini, Marta, Law, Randall, Guidorzi, Laura, Pacheco, Claire, Sturari, Sofia

2025

Overview

This work presents an upgrade to the methodology adopted to investigate the provenance of the raw lapis lazuli material used in antiquity for carving precious artefacts. Samples from archaeological excavation contexts frequently display superficial degradation processes affecting the crystals of the mineral phases useful for provenance attribution (especially pyrite). To address this issue, an innovative workflow has been developed, centred on the application of X-ray micro-computed tomography (μ-CT) and micro-ablation treatments with a pulsed laser source prior to investigation with ion beam analysis (IBA). High-resolution μ-CT is employed to evaluate the alteration state of pyrite crystals within the entire volume of the lapis lazuli rock, and, if required, to identify the most suitable crystals on the surface for subsequent laser treatment. The micro-ablation procedure aims to create a small breach in the superficial altered layer (the irradiated areas are approximately 65 × 65 μm 2 ), thereby exposing the preserved crystal beneath and allowing for the analysis of its trace element contents with IBA. The methodology of the workflow is presented, together with its first application to archaeological lapis lazuli material: three precious beads from the ancient Royal Cemetery of Ur (Mesopotamia, 3rd millennium BCE). The results are complemented by the application of a provenance protocol already validated that proved, for the first time using a micro-invasive analytical approach, a match between the Afghan quarry district and the raw material used to carve these beads.

• Publisher: Springer Berlin Heidelberg,Springer Nature B.V
• Subject: Ablation / Applied and Technical Physics / Archaeology / Atomic / Complex Systems / Computed tomography / Condensed Matter Physics / Crystals / Cultural heritage / Excavation / Focus Point on Advances and Innovation in Heritage Science / Investigations / Ion beams / Laser ablation / Lasers / Mathematical and Computational Physics / Methodology / Minerals / Molecular / Optical and Plasma Physics / Physics / Physics and Astronomy / Pulsed lasers / Pyrite / Raw materials / Regular Article / Theoretical / Tomography / Trace elements / Workflow