This content was first published on IGR – Italian Gemological Review no. 21 in 2025. The information provided here is therefore current as of the original publication date.
In the world of corundum, the distinction between rubies and pink sapphires is a central theme in gemology, as both gems, although varieties of the same mineral, have unique characteristics due to different impurities and conditions of formation. George Frederick Kunz was among the first to systematically study colored varieties of corundum in the late 19th century, describing the relationships between chemical composition and color shade in rubies and sapphires. On the modern scene, Richard W. Hughes has expanded this knowledge with his volume “Ruby & Sapphire: A Gemologist’s Guide”, considered one of the most comprehensive texts on rubies and sapphires, bringing together decades of field experience and detailed analytical investigations.
The classification of a corundum as a ruby or pink sapphire is based primarily on its chromium oxide (Cr2O3) content. Generally, Cr2O3 values between 0.1 and 3.0 wt% impart the red coloration typical of rubies, while concentrations below about 0.1 wt% keep the gem in the pink sapphire category. However, at reference institutions such as the SSEF, there is no strict, universally applicable threshold; rather, the separation between ruby and pink sapphire is based on observation of chromatic saturation and comparison with standard chromatic “master stones”.
In recent decades, advances in analytical techniques — from FTIR, Raman, and UV-Vis-NIR spectroscopy to analysis by LA-ICP-MS — have enabled increasingly precise characterization of impurities and inclusions, offering fundamental tools for identifying the geographic origin and assessing the value of gemstones. These advanced methodologies not only highlight intrinsic chemical differences, but also allow reconstruction of geological history and formation conditions, crucial elements for proper authentication and traceability.
A recent study entitled “Color Mechanism Analysis and Origin Comparison of Pink-Purple Sapphires from Vietnam and Madagascar”, conducted by Qiurong Guo, Pengyu Li, Mingying Wang, Siyi Zhao, Sichun Yang and Guanghai Shi and published in Crystals (2025) analyzed pink-purple sapphires from Vietnam and Madagascar to identify their provenance by gemological tests, microscopic observations, spectroscopy (FTIR, Raman, UV-Vis-NIR) and LA-ICP-MS. The Vietnamese samples showed hazy appearance and orange iridescence, while the Malagasy samples had a more intense purple hue. The pink color is due to Cr3+, but in the Malagasy samples Fe3+ and Fe/Ti transitions intensify the blue, turning to purple. Vietnamese inclusions include white and blue bands, turbid inclusions, calcite and apatite, while Malagasy inclusions have zircon. Chemically, the Vietnamese samples had less V, Mg, Ga and more Fe, while the Malagasy samples had less Fe and more Ga. The results reveal significant differences in inclusions and chemical composition, providing useful tools for gemological traceability. In particular, the study highlights the role of chromium in coloration and the influence of other elements such as iron, titanium and vanadium, as well as the peculiarities of inclusions as indicators of origin.
For further reading:
https://www.mdpi.com/2075-163X/11/7/750
https://www.mdpi.com/2075-163X/10/7/597
https://www.ssef.ch/wp-content/uploads/2019/07/EGS-2019_MSK_final_web.pdf
Gem news published on IGR – Italian Gemological Review #21 – Autumn 2025.
