The second-to-last issue of the Journal of Gemmology (Volume 40, no.1, 2026) presents a series of studies that push the boundaries of gemological characterization, integrating multiscale mineralogical analysis, advanced geochemistry, and artificial intelligence algorithms to address the challenges of an increasingly complex market. From opalised woods of Indonesia to emerald sources in central China, through to metamorphic quartzes from Tanzania, the volume offers a scientific panorama of extraordinary variety.
The study “Green Opalised Wood from West Java, Indonesia” by Maxence Vigier, Simon Gouzy, Benjamin Rondeau, and Emmanuel Fritsch describes a rare variety of green opalised wood recently discovered in the Garut region of West Java. Multiscale analyses conducted using XRD, Raman, SEM, and TEM revealed that the material is composed primarily of opal-CT, with the unusual green colour attributed to glauconite/celadonite inclusions dispersed throughout the matrix. The vivid green luminescence under UV light is instead caused by the presence of uranyl groups.
Yu-Yu Zheng, Bo Xu, Xiao-Yan Yu, Shi-Yuan Cui, Zi-Liang Zhang, Le Li, and Ying Yan, in “Emerald from Zhen’an (Shaanxi, Central China): Gemmological Characterisation and Origin Determination Using Machine Learning”, document a new and promising emerald source in the Zhen’an district of Shaanxi Province. These V-dominant specimens display distinctive geochemical characteristics, including high caesium and gallium levels and low iron levels, which clearly differentiate them from other world sources. A notable methodological innovation is the application of machine learning algorithms — specifically the XGBoost model — to distinguish these emeralds from those of eight other localities, achieving a classification accuracy of 98.52%.
In “Rose Quartz from the Hamedan Region, Western Iran: Mineralogy and Gemmology”, Nazanin Barzegar, Mohammadreza Hosseinzadeh, and Vartan Simmonds present for the first time gem-quality rose quartz from western Iran, extracted from pegmatitic dykes. The characteristic pink-violet colouration is attributable to fibrous micro-inclusions of a dumortierite-like phase, with the colour generated by Fe²⁺–Ti⁴⁺ charge transfer within these inclusions.
The study “Discovery and Characterisation of ‘Jaguar’ Quartz from Tanzania”, by Alessandra Altieri, Giorgia Confalonieri, Giovanni O. Lepore, Marco Torelli, Carmine Allocca, and Michele Macrì, describes a new variety of quartz named “Jaguar”, discovered at the end of 2022 in the Mpwapwa district, Tanzania. It consists of rock crystal with inclusions of phlogopite and rose quartz containing magnesio-hornblende. These dark inclusions, which vary morphologically from tabular and pseudo-hexagonal (phlogopite) to prismatic and elongated (hornblende), often show a preferred orientation within the host material, giving the gems a distinctive appearance suitable for designer jewelry.
Analyses conducted using electron probe microanalysis (EPMA) and powder X-ray diffraction (PXRD) confirmed the syngenetic origin of the inclusions. In particular, phlogopite likely crystallized during early fluid-rich stages, while magnesio-hornblende formed later at higher temperatures, reflecting the thermal and chemical evolution of the Mpwapwa geological system. Unlike many rose quartzes typically associated with pegmatitic environments, “Jaguar” quartz has a clearly metamorphic origin, making it a traceable gemological material of significant interest for the collectors’ market.
The technical sections of the issue further enrich the scientific picture. The Gem Notes document mineralogical rarities such as yellow austinite from Mexico and colour-change blue gahnite, as well as critical identification cases: among these, a metamorphic sapphire displaying the FTIR bands of the “3309 cm⁻¹ series” — normally indicative of heating — yet retaining intact diaspore inclusions, suggesting that the temperature did not exceed 500 °C. Also reported is a ruby treated with an unusual barium- and zirconium-bearing glass, and introduced is “Crysilliz,” a new synthetic material made of polycrystalline pure silicon with a metallic lustre.
