Physico-chemical characterization of diopside in lapis lazuli: a study from luminescence activators and quenchers to material provenance investigations
The topic of this PhD project follows one the main lines of research of the group, the provenance determination
of lapis lazuli used in antiquity.
Diopside, a mineral of the pyroxene group, is one of the main mineralogical phases present in this semi-precious blue stone and its elements contained in
traces can determine the original quarry [Re 2011].
As of now we own rocks from 5 different provenances (Afghanistan, Tajikistan, Siberia, Myanmar and Chile), forming a database of more than 100 samples.
For provenance purposes, two mineralogical phases are mainly investigated, diopside and pyrite, using a multi-technique approach described in [Lo Giudice 2009] and in
particular with the simultaneous acquisition of Ionoluminescence (IL) and Particle Induced X-ray Emission (PIXE) spectra. As the target crystals can be very
small (around 100 micrometer in diameter), the use of a microbeam is mandatory. The IL signal of diopside can also be characteristic to the specific origin, both in
peak positions and intensities; the study of correlations between the distinctive luminescence peaks and possible activators and quenchers present in traces
can shed new light on provenance issues, as it would strengthen some of the "weaker markers" identified in our established provenance protocol [Lo Giudice 2017].
The majority of our data is acquired in the frame of ALCHIMIA project at the Legnaro National Laboratories of the National Institute of Nuclear Physics
(INFN-LNL). In addition, a new project SIBILLA, specifically dedicated to this topic, has been developed via the international
IPERION CH/IPERION HS programmes to perform the analyses at the
AGLAE accelerator facility of the Louvre Museum (Paris, France). One of the advantages of this facility is
the opportunity to analyse as well precious historical artefacts, as the measurements are performed in air. Collaborations with archaeologists are ongoing
for the examination of carved lapis lazuli going back to the III millennium BC. Moreover, the possibility of using SEM-WDS elemental analysis as an
alternative to PIXE for reference samples (measurements carried out at Okayama University, Japan) is currently under study.
Multivariate analysis is then applied to investigate all the resulting data, starting from unsupervised methods such as Principal Component Analysis up to
supervised methods of classification and regression.
In the figures are shown respectively: a small fragment of lapis lazuli (about 1 cm long) from an archaelogical site and and measurements at the AGLAE accelerator
facility.
