Aurélien Delaunay

A series of tourmalines from Abuloo, Oromia regional state, Ethiopia, was studied to describe their chemical and spectroscopic characteristics. Data from the seven samples were consistent with elbaite. Several specimens contained significant concentrations of copper (up to 2.29 wt%) and iron up to 0.81 wt%. Visible absorption spectroscopy indicated that the blue coloration in most samples is primarily related to Cu, with Mn and Fe contributing to a lesser extent, whereas in some specimens, Fe is the chromophore dominating Cu. The Cu-dominant tourmalines exhibited characteristics that correspond to the gemological definition of Paraíba tourmaline. Elements such as Ga, Pb, Bi, Zn, and V, as well as REE and Cu, could help to distinguish Ethiopian samples from copper-bearing tourmalines from Brazil, Mozambique, and Nigeria. These results suggest that the Abuloo occurrence represents a potentially significant source of gem-quality, unheated Cu-bearing tourmaline with distinctive features that may aid in its identification.

Fifteen opal samples of gem quality from the Spencer Opal Mines in Idaho (USA) were examined. These opals display play-of-colour, with three of them having a pink body colour. The analysis was conducted using standard gemmological tools, along with non-destructive spectroscopic, chemical, and imaging methods. All samples were identified as opal-A, with their play-of-colour resulting from a regular stacking of hydrated silica spheres. However, at times, the spheres are large to allow diffraction. Opal-A are only occasionally found in nature as gems. Inclusion observed in the studied samples included alunite (KAl₃(SO₄)₂(OH)₆), anhydrite (CaSO₄), and iron-rich spherules (hematite). The pink body colour in the studied specimens is caused by the scattering of light from reddish dendrites. The samples show significant stratification, with fluorescence ranging from green to blue to orange, the latter of which represents a new phenomenon in opals not associated with quinones. Additionally, the orange fluorescence is accompanied by emissions from Sm²⁺ in anhydrite inclusions.

Studies on emeralds from Habachtal (Austria) are scarce and non-exhaustive. However, they represent a significant interest to the community, as they have been assumed to be present in historical pieces of jewelry. Along with Egypt, Habachtal is suggested to be one of the main sources of gem-quality emeralds of archaeological significance. In this regard and due to their similar macroscopic look and geological context, it has always been challenging to distinguish Austrian and Egyptian emeralds set in historic jewelry. In this paper, a first comprehensive study of several Habchtal emeralds is presented based on a combination of classic gemology, chemistry and spectroscopy, using non-destructive to micro-destructive methods. Spectroscopic analyses, such as via Raman, FTIR and UV-Vis–NIR spectroscopies, showed that emeralds from Habachtal (Austria) contain Type II H₂O molecules with alkalis and they are colored by chromium and iron, similarly to emeralds from Egypt. Under an optical microscope (and identified by Raman spectroscopy), actinolite needle-like inclusions are frequently observed in Austrian emeralds. Other inclusions, such as quartz, plagioclase, albite, phlogopite and pyrite, can also be observed in Austrian samples. Chemical analysis of Austrian emeralds’ trace elements by LA–ICP–MS show similar results to those from Egypt, with the exception of V, K and Rb, which show a lesser content in Austrian emeralds. Thanks to the determination of inclusions combined with a careful examination of specific chemistry, this study shows that Austrian emeralds can be distinguished from their Egyptian counterpart.

The present study is focused on the analysis of zircon inclusions found in pink to purple sapphires from Ilakaka (Madagascar) with an optical microscope, Fourier-transform infrared (FTIR), and micro-Raman spectroscopy in order to update previous knowledge and find insights to separate heated from unheated samples. In total, 157 zircon inclusions in 15 unheated samples and 74 zircon inclusions in 6 heated samples are analysed using micro-Raman spectroscopy with standardised parameters. The full width at half maximum (FWHM) of the main Raman band due to anti-symmetric stretching vibration ν₃ of the SiO₄ tetrahedron in the zircon structure has been carefully measured. In the unheated samples, it ranges from 6.26 to 21.73 cm⁻¹ with an average of 10.74 cm⁻¹, a median of 10.04 cm⁻¹, and a standard deviation of 2.84 cm⁻¹. On the other hand, it is lower in the heated samples, ranging from 4.83 to 14.97 cm⁻¹ with an average of 7.23 cm⁻¹, median of 7.06 cm⁻¹, and standard deviation of 1.63 cm⁻¹. In our unheated samples, the FWHM was rarely below 7 cm⁻¹. In our heated samples, the FWHM was rarely above 12 cm⁻¹ but mostly below 8 cm⁻¹, with a variation restricted to less than 3 cm⁻¹ in the same sample. The present work will hopefully further contribute to more accurately identifying the low-temperature heat treatment of pink sapphires from Ilakaka, Madagascar.

In the present study, rough emerald single crystals and rough emeralds in the host rock from the ruins of Alexandria and from the Mount Zabargad in Egypt, preserved in the collection of the museum of the Ecole des Mines (Mines Paris—PSL) since the late 19th or early 20th century, are investigated. All samples were characterized by non-destructive spectroscopic and chemical methods during a week-long loan to the LFG. Raman, FTIR and UV-Vis-NIR spectroscopy revealed that Egyptian emeralds contain H₂O molecules accompanied by relatively high concentrations of alkali ions and are colored by chromium and iron. Additionally, EDXRF showed that the emeralds from Egypt contain up to 84 ppm Rb and low amounts (below 200 ppm) of Cs. Inclusions and parts of the host rock were also observed under optical microscope and analyzed with Raman spectroscopy. Tube-like structures, quartz, calcite, dolomite, albite and phlogopite are associated minerals, and inclusions are identified in these historic emeralds from Egypt. This work will hopefully further contribute to the characterization of emeralds of archaeological significance.