An innovative approach for provenancing ancient white marbles: the contribution of x-ray diffraction to disentangling the origins of G\xf6ktepe and Carrara marbles

F Antonelli,F Nestola

doi:10.1038/s41598-021-01800-7

Abstract

The paper presents a very efficient, quick, low-cost and minimally micro-destructive approach to discriminating between Roman artefacts sculpted with Göktepe (Aphrodisia, Turkey) or Carrara (Apuan Alps, Italy) white marbles by using a standard X-Ray Powder Diffractometer (XRPD) and a refinement of the unit cell parameters and volume of calcite. At present, the routine way of differentiating between these two almost indistinguishable by-eye marbles is based on the typically higher strontium content of calcite in the Microasiatic lithotype, a unique geochemical-crystallographic feature with respect to all other non-Göktepe fine-grained white marbles used in classical times. The XRPD approach has been verified by testing eighteen samples of known composition, nine from Carrara and nine from Göktepe quarries, which had already been analysed with other laboratory techniques. The applicability of the method to archaeological artefacts was confirmed by an archaeometric study performed on some famous Roman sculptures of the National Archaeological Museum of Venice and from Hadrian’s Villa at Tivoli. The results show that Göktepe/Carrara discrimination is always possible and that this XRPD approach can potentially become a useful and low-cost routine procedure to solve provenance issues.

Highlights

This paper aims to describe a quick, low-cost and only minimally micro-destructive approach able to distinguish between Göktepe and Carrara marbles on the basis of their dissimilar basic mineralogy as revealed by the X-ray powder diffraction (XRPD) technique
As we remarked in the introduction, marbles from Göktepe generally show much higher Sr contents; Sr is a larger cation than Ca and this should cause a slight but detectable increase in the unit-cell parameters and volume of calcite
Though this first general mineralogical difference was very easy to observe by X-ray powder diffraction, account must be taken of the fact that, albeit very rarely, some varieties of Carrara marble can contain pure calcite; this can restrict the chance of safe discrimination between the two marbles by using only the qualitative XRD technique

Summary

Introduction

We can state conclusively that the high Sr content within the calcite crystal structure from Göktepe samples increases the unit-cell volume slightly but significantly with respect to calcite in Carrara samples allowing a very easy identification between the two types of marbles regardless of all other minor minerals that could be present in the rocks from both the localities.

Results

Conclusion