Dear American Mineralogist Readers, Below are the Paper Highlights for this month’s issue of the American Mineralogist: International Journal of Earth and Planetary Materials. You may also view the American Mineralogist Paper Highlights list at https://msaweb.org/MSA/AmMin/ and click the “Editor’s Notes” tab, which will be available shortly after the issue is live. The DOI links below will take you to the abstract on GeoScienceWorld. If you have “IP” access via your institution’s library, it should reveal the whole paper. Consult your institution’s IT department or friendly librarian. If you have an MSA membership, authenticate your login from the American Mineralogist website at http://www.msapubs.org/. On the portal page, click the American Mineralogist link and enter your username (e-mail address) and your password (membership number). Then, search for the paper you want to read via your browser's search tools. (On most PCs, it is control-F, but that may vary for you.) Note that on GSW, you can sign up for a table of contents to be sent to you when the issue is live -- this feature is available to anyone who registers on the site. Thank you for reading American Mineralogist. Sincerely, Fabrizio Nestola Paul Tomascak Editors, American Mineralogist American Mineralogist Volume 111; Number 4; 04-01-2026 Using delayed nucleation in melt inclusions to constrain final growth durations of magmatic crystals: An introduction and example using the May 18, 1980, White Pumice of Mt. St. Helens Don R. Baker Observations of the presence or absence of crystals in melt inclusions of the same composition, but different volumes, can be combined with classical nucleation theory models of nucleation in small volumes to constrain the duration between the time melt inclusions became supersaturated and their quenching to conditions where crystal formation was no longer possible. https://doi.org/10.2138/am-2024-9353 Mixing thermodynamic model of Au-Ag Alloys in gold deposits established by a modifier double defect method Feng Lai, Qingfei Wang, Deru Xu, Mingxing Ling, Shuo Yin, and Shaohao Zou Lai et al. obtain comprehensive and consistent mixing properties for Au-Ag alloys across a temperature range of 200 to 1300 K. Epithermal and orogenic deposit conditions result in different compositional distributions of Au-Ag alloys. The composition of Au-Ag alloys can serve as an indicator in gold exploration. https://doi.org/10.2138/am-2024-9663 Growth rims in uraninite: Evidence of episodic changes in hydrothermal fluid composition in the Rohil uranium deposit, Rajasthan, India Ajoy K. Padhi, Mrinal Kanti Mukherjee, B.S. Bisht, and B. Saravanan Unlike in zircon and garnet, growth rims and oscillatory zoning are not well documented in uraninite, possibly because of their rarity. Uraninite is a chemically active mineral and may change its composition as it recrystallizes during interaction with fluids. There is a paucity of information on compositional variations in uraninite, where concentration gradients in U, Th, and Y; U-Th sector zoning on crystal faces; dissolution by bornite; alteration by Si and Ca; and contrast in composition of the growth rims of uraninite have been studied. The importance of the present paper lies in attempting for the first time to document, quantify, characterize, and analyze the growth rims of uraninite, a relatively rare phenomenon, and to link the evolution of hydrothermal fluid that affected the uranium mineralization with the growth rims, especially in a poly-metallic setup. Such findings can help to constrain and characterize conditions of uranium mineralization in a polymetallic setup and would broadly help in exploration guidance. https://doi.org/10.2138/am-2024-9669 Myrmekite and antiperthite formation in deformed granite: Chemical and crystallographic constraints on formation mechanisms Yueting Song, Thomas A. Griffiths, Shanrong Zhao, and Rainer Abart Myrmekite and antiperthite served as reaction partners exchanging chemical components in deformed granite. Silica was transferred from strained magmatic or myrmekitic quartz to unstrained myrmekitic quartz. Crystallographic orientation relationships between quartz and feldspar can reveal the growth features and evolution stages of myrmekite. A similar approach can be applied to study intergrowths with constituent minerals sharing incomparable structures. https://doi.org/10.2138/am-2024-9715 Framework for a volume model for monoclinic amphibole Carl Swindle, Paul Asimow, Roberta Oberti, Massimo Boiocchi Swindle et al. calibrated a volume model for amphiboles as a function of composition and cross-site ordering that allows for the incorporation of minor components. As volume is the pressure derivative of Gibbs energy, assessment of these differences over large pressure differentials is crucial for modeling purposes in MELTS. The effects of composition on volume are important for thermodynamic modeling of magmatic systems, assessing whether a crystal will sink or float in a magma chamber, establishing how amphibole compositions influence seismic wave velocities, and more. https://doi.org/10.2138/am-2024-9728 Deep-UV micro-Raman spectroscopic estimates of peak metamorphic temperatures using rock chips bearing carbonaceous material Yoshihiro Nakamura, Koji U. Takahashi, and Shunya Kaneki This paper reports on a novel analytical method for non-destructive peak metamorphic temperature estimates (PMTs) of carbonaceous material (CM) bearing rock chips with deep-UV micro-Raman spectroscopy. The method, combining deep-UV micro-Raman spectroscopy with Python-based peak deconvolution, enables precise estimation of peak metamorphic temperatures, covering a wide range of PMTs from 83 to 555 °C, with no sample preparation. https://doi.org/10.2138/am-2025-9766 Formation of low-Ti and high-V magnetite in iron oxide-apatite mineralization by fluid-aided alteration: Insights from Baixiangshan deposit, Eastern China Hao Hu, Daniel Harlov, Xiao-Dong Deng, Wan-Ting Li, Zhuang Duan, Zhe-Jian Pan, and Jian-Wei Li The low-Ti and high-V magnetite grains generally have a triple junction texture with Ti-bearing minerals along their grain boundaries, implying that it has been recrystallized by later-stage fluids, and Ti has been leached out to form Ti-bearing minerals. Many other low-Ti and high-V magnetite grains from IOA deposits worldwide may also have secondary origins. The Ti+V vs. Fe new discrimination diagram is useful to distinguish between primary and metasomatically re-equilibrated magnetite in IOA deposits and probably other high-temperature hydrothermal systems in general. https://doi.org/10.2138/am-2025-9782 Crystal-chemical variations of celadonite in relation to glauconite Jongkyu Park, Il-Mo Kang, Sung Man Seo, Jaehwan Kim, Sang-Gun No, Seungbin Seo, and Jiyeon Joo The concentration steps for the Janggi celadonite were systematically monitored and evaluated using XRD patterns, Rietveld refinement, and compositional analysis. The Janggi celadonite is classified as celadonite-aluminoceladonite. The composition variation of celadonite is governed by a three-site heterovalent substitution mechanism: ivAl3+ivSi4+–1vi(Fe3+total,Al3+)1.58viMg2+–1.5xiiNa++0.25xiiK+–1. Celadonite accommodates the structural misfit between tetrahedral and octahedral sheets differently from glauconite, due to the wide range of ionic sizes in the celadonite octahedral sheet. Celadonite may have a broader range of b-axis variations than previously recognized, suggesting greater structural flexibility. The key differences between celadonite and glauconite lie in their octahedral cation composition, substitution trends, charge distribution, and misfit accommodation styles and unit-cell parameters. https://doi.org/10.2138/am-2025-9787 Long-range modulation in uranium-bearing hematite superstructure constrained from STEM analysis and ab initio calculations Jie Yao, Cristiana L. Ciobanu, Nigel J. Cook, Kathy Ehrig, Ashley D. Slattery, Eugene S. Ilton, Nobuyoshi Miyajima, and Gerd Steinle-Neumann This paper addresses the nature of superstructuring in uraniferous hematite, using transmission electron microscopy and ab initio calculations. The experimental 12-fold, long-range modulation was reproduced using an empirical hematite superstructure model with variable Fe occupancy. An excellent match is observed between the model, electron diffraction patterns, and images. A further simplified Fe and O vacancy scheme is employed, involving a double-corner Fe vacancy environment constrained for pentavalent U from prior ab initio simulations and localized O vacancies for charge balance. The authors’ assessment of the relaxed superstructure shows a good match with analytical data. Moreover, calculated Bader charge and magnetic moment validate the inference of U5+ incorporation into the hematite superstructure, and formation energy calculations show how the superstructure is stabilized by the presence of U relative to the vacancy defect structure. Combining ab initio calculations and STEM analysis for U incorporation in Fe-oxides is valuable for the long-term storage of radioactive waste as much as for optimized, low environmental impact exploitation of uranium-bearing ores. https://doi.org/10.2138/am-2025-9794 Selective adsorption of magnesium ions and structural reconstruction in acidified palygorskite Yi Zhou, Guocheng Lv, Shijun Huo, Xiaotong Yang, Meng Liu, Lijuan Wang, and Libing Liao This study reveals that acid-modified plagioclase (Plg) exhibits enhanced Mg2+ selectivity (100× over Li+) via charge/ligand interactions and structural reorganization, enabling efficient Mg-Li separation for lithium extraction from brines. Acid-driven dissolution-reprecipitation processes create dynamic interfaces regulating ion entrapment and migration, linking mineral recyclability to contaminant mobility and geochemical resilience. These findings advance sustainable strategies for critical resource recovery (Li/Mg) and weathering system dynamics. https://doi.org/10.2138/am-2025-9834 Fe-Ti vs. Fe-Fe charge transfers: A comprehensive review and its applications in minerals and glasses Maxence Vigier, Helen Evans, George R. Rossman, Stéphane Jobic, and Emmanuel Fritsch Vigier et al. studied in detail the Fe2+-Ti4+ (Fe-Ti) and Fe2+-Fe3+ (Fe-Fe) charge transfers (CT). This phenomenon has been known for many years in minerals and glasses to induce mostly a brown to black color. Very often, authors hesitate between Fe-Fe and Fe-Ti charge transfer to interpret absorptions leading to a blue color. Hence, the authors’ choice to group these two charge transfers. To date, there is no comprehensive work that gathers and rationalizes all the information regarding Fe-Ti and Fe-Fe CTs in materials. The authors aimed to establish criteria to identify the potential presence of an Fe-Ti and Fe-Fe CTs. Faced with the observation that some minerals can exhibit several absorption bands related to this transfer, Vigier et al. then investigated a correlation between the position of the CT absorption band and the distance separating the Fe and Ti atoms, or the two Fe atoms, within the crystal structure. These correlations offer a promising method to identify the Fe-Ti CT and to separate it from a Fe-Fe CT in many cases. https://doi.org/10.2138/am-2025-9835 Using machine learning for automatic rock classification Tamanna, Dominik C. Hezel, Nishtha Srivastava, and Johannes Faber Tamanna et al. research how we can use machine learning (ML) to classify rocks. Keeping to the TAS plot framework, the authors add 7 additional major and minor element oxides and consider 3 cases where we have all 10 major and minor element oxides; rocks for which no SiO2 concentrations have been reported, cases with solution-based techniques; and rocks in which alkali element concentrations were affected by, e.g., secondary or late-stage hydrous alteration. The model’s real-world application is its ability to classify rocks for which no SiO2 data are reported and handle the classification of altered rocks, although to a lesser extent. It also serves as a test of the extent to which ML can be applied to such classification problems. This study highlights the potential of ML for geochemical classification and lays the groundwork for similar, more complex applications in the future, such as automatic mineral classification. https://doi.org/10.2138/am-2025-9958