The Winter 2025 edition of Gems & Gemology (Volume 61, Issue 4) offers an in-depth analysis of some of the most current topics in the gemological landscape, from the discovery of new primary sapphire deposits in Montana to the identification of Chinese emeralds from a newly documented source, through to the scientific reassessment of Arkansas turquoise.
In “The Primary Sapphire Occurrence at French Bar Sill Along the Missouri River, Near Helena, Montana”, researchers Robert E. Kane, Kory L. Pettman, Aaron C. Palke, Rachelle B. Turnier, Richard B. Berg, Nathan D. Renfro, and Christopher P. Smith document the first primary sapphire deposit in Montana outside the celebrated Yogo Gulch. The site, identified as an Eocene-age basaltic trachyandesite, was studied through the analysis of 80 sapphires still embedded in the host rock. The study reveals that the trace element chemistry and inclusions of these sapphires overlap almost entirely with those of the alluvial deposits of the Missouri River, with one key distinction: while approximately 25% of the alluvial sapphires contain spinel, those from French Bar Sill show exclusively biotite mica inclusions. Although the site is considered more of a scientific curiosity than a commercially viable mine, its value lies in the new insights it provides into the genesis of Montana sapphires.
In the article “Characterization of Emeralds from Zhen’an County in Shaanxi, China”, Yi Guo, Xiao-Yan Yu, and Yu-Yu Zheng present a detailed analysis of a new emerald source discovered in 2017 in the Qinling orogenic district of China. These specimens are distinguished by having vanadium as the primary chromophore ion, with notably low chromium concentrations — a characteristic that sets them apart from many other world sources. Analyses using Raman spectroscopy and LA-ICP-MS identified a high gallium/cesium ratio as a diagnostic indicator for distinguishing these emeralds from those of the Chinese Malipo deposit, along with the presence of abundant two-phase fluid inclusions and distinctive zigzag growth lines.
Finally, Alexander A. Goodsuhm in “An Evaluation of Turquoise from the Mona Lisa Mine in Arkansas” scientifically reassesses the Mona Lisa mine, located in the Ouachita Mountains, as a commercial source of turquoise. The research confirmed the authentic nature of the extracted material, with copper oxide concentrations ranging from 1.71 to 6.18 wt.%, mineralized within fractures in altered novaculite — a geology entirely unique for this type of deposit. The samples range from chalky turquoise requiring stabilization to harder, more saturated specimens that can be cut and polished directly.
The issue is enriched by the usual in-depth sections. The Lab Notes document the first case of faceted Armenite received by a GIA laboratory, a 100-carat cuprite crystal with malachite inclusions, and new methodologies for detecting fracture-filled diamonds set in jewelry. The Micro-World section explores tubular inclusions resembling a “bamboo forest” in Colombian emeralds and “worm-shaped” heulandite crystals in Ethiopian opals. Gem News International reports a summary of presentations from the Converge 2025 conference, highlighting new red garnet production from northern Vietnam and the spread of fraudulently reconstructed minerals in Pakistan.
The complete edition of Gems & Gemology Winter 2025 is available on the official website.
