Reliability of LA-ICP-MS and synchrotron XANES for provenance identification of rubies

Abstract

Modern gemological laboratories face significant challenges in determining the geographical origin of rubies, requiring careful analysis of inclusions, trace element chemistry, and spectroscopic data. In this work, trace elements of rubies from Myanmar, Madagascar and Mozambique were investigated by using the LA-ICP-MS technique. The iron concentration in the rubies from Madagascar and Mozambique are higher than 1000 μg/g while the titanium concentration is less than 5 μg/g. In the Myanmar marble-hosted ruby, the iron concentration is below 10 μg/g while titanium concentration of a few thousands' μg/g is generally detected. The X-ray absorption near edge structure (XANES) spectra were taken from the high iron containing and marble-hosted rubies for obtaining the chemical information of iron and titanium, respectively. The XANES spectra reveals that trivalent iron is the major species in rubies of high iron rubies. Similarly, Cr K-edge XANES spectra are obtained for Cr³⁺ in rubies from two different sources. Ti K-edge XANES spectra in ruby from Myanmar show a 4+ oxidation state, and its XANES spectrum resembles that of TiO<inf>2</inf> with a rutile phase.