American Mineralogist October 2025 issue paper highlights 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 is a feature open to anyone who registers on the site. Thank you for reading American Mineralogist. Sincerely, Hongwu Xu Paul Tomascak Editors, American Mineralogist American Mineralogist Volume 110; Number 10; 10-01-2025 Natrojarosite formed in the Matanomadh Formation, Kutch, India: A Na analog of jarosite on Mars Dwijesh Ray, Aditya Das, Subham Sarkar, Satadru Bhattacharya, Chandrani Nayak Ray et al. discuss the mineralogy and spectroscopy of iron sulfates, abundant secondary minerals discovered on Mars using orbiter instruments and in situ rovers. The new terrestrial analog sites, similar to those in the Martian volcanic terrain, are important to validate the Mars orbiter data and to better understand the complexity of formation history until samples are returned from Mars. The Fe K-edge XANES and EXAFS analyses help to ascertain the Fe speciation and the past aqueous environment of Mars. This study could inform future landing sites on Mars. https://doi.org/10.2138/am-2024-9360 EBSD mapping of Cu-Fe-sulfides reveals microstructures enriched in critical/precious metals and resolves deformation histories Samuel A. King, Nigel J. Cook, Cristiana L. Ciobanu, Kathy Ehrig, Yuri Tatiana Campo Rodriguez, Sarah Gilbert, Animesh Basak King et al. characterized chalcopyrite and bornite from the Olympic Dam Cu-U-Au-Ag deposit using EBSD to identify microstructures and their correlations with trace element concentrations measured by LA-ICP-MS. Natural chalcopyrite is shown to be a rich source of micro-structural and -textural information, preserving <110> and <001> crystallographic preferred orientations, {110} and {112} twin systems, grain boundary migration, foam textures, and subgrain boundaries. The oriented stress imposed by brecciation and/or fluid fluxes at Olympic Dam, alongside temperature, pressure, and strain rate, induce a variety of microstructures preserved in chalcopyrite. EBSD mapping reveals that what appears as single grains of chalcopyrite in reflected light is, in fact, aggregates composed of ~100 individual grains. In contrast, analyzed bornite displays overwhelming crystallographic homogeneity. These observations confirm the critical role played by microstructures in Cu-(Fe)-sulfides as traps for Pb, a non-target contaminant in copper concentrates, as well as new evidence for the physical state of Ag and potential value-add critical metals like Bi and Sb. https://doi.org/10.2138/am-2024-9396 Moxuanxueite, NaCa6Zr(Si2O7)2OF3, a new wöhlerite-group mineral from Gejiu alkaline complex, Yunnan Province, China Kai Qu, Guochen Dong, Ting Li, Guang Fan, Xiangping Gu, Yufei Wang, Yanjuan Wang Qu et al. describe moxuanxueite, ideally NaCa6Zr(Si2O7)2OF3, a new Zr-disilicate that was discovered in the Gejiu alkaline complex. Moxuanxueite offers important insights into the chemical variability of wöhlerite-group minerals. Furthermore, moxuanxueite, as well as other wöhlerite group species, as the common accessory Zr-Nb-Ti-bearing minerals, are not only important in understanding the crust-mantle cycle of HFSE elements but are also of economic interest as a promising source of critical metals. https://doi.org/10.2138/am-2024-9397 Rare occurrence of jarosite-alunite solid solutions with intermediate Al-Fe contents in the Jurassic Aztec Sandstone, Nevada, U.S.A. Thomas M. McCollom, Sally L. Potter-McIntyre, Chris Donaldson, Andres Reyes, Bruce Moskowitz, Peter Solheid McCollom et al. report the discovery of Al-Fe solid solutions with compositions intermediate between alunite and jarosite in sandstones from Nevada, which constitutes only the third geologic setting where such solid solutions have been documented. The results provide further evidence that Al-Fe solid solutions in this mineral group can occur in natural environments and may lead to new insights into the conditions that allow precipitation as solid solutions rather than end-members. https://doi.org/10.2138/am-2024-9423 Laboratory synthesis, spectroscopic characteristics, and thermal behavior of phoxite Wenxi Chen, Xiaohui Fu, Zhongchen Wu, Jiang Zhang, Guobin Jin, Lingxi Zhang, Wang Liu Chen et al. report the FTIR and VNIR spectra, and thermal behavior of phoxite. The formation of phoxite prefers high relative humidity conditions (RH >59%). Phoxite can be a new biomarker mineral and an indicator of habitable environments. https://doi.org/10.2138/am-2024-9463 Theoretical studies of thermodynamic and elastic properties of diamond under Earth’s mantle conditions Xu Zheng, Joshua M.R. Muir, Yi Wang, Jiajun Jiang, Qianxi Chen, Feiwu Zhang Zeng et al. report that diamonds exhibit pronounced elastic anisotropy and nonlinear responses to pressure and temperature. Diamonds can significantly alter seismic velocities due to their lower density and higher moduli compared to typical mantle materials, suggesting that their presence could be detectable via advanced seismic techniques. The distinctive seismic signatures of diamonds at high pressures and temperatures, as predicted by this study, offer a novel approach to probe deep Earth and potentially other planetary interiors. This could lead to better understanding and exploration of the mantle’s geological features, aiding in the study of planetary evolution under extreme conditions. https://doi.org/10.2138/am-2024-9574 Nigelcookite, PbFe2(2+)V2(3+)(PO4)3(OH)3, and plumbojohntomaite, PbFe2(2+)Fe2(3+)(PO4)3(OH)3, two new minerals of the bjarebyite group from the Yushui Cu deposit, South China Wei Yao, Peng Liu, Guowu Li, Ningyue Sun, Wenqiang Yang, Chao Zhang, Wenlei Song Yao et al. report two new members of the bjarebyite-group minerals, nigelcookite, PbFe2(2+)V2(3+)(PO4)3(OH)3, and plumbojohntomaite, PbFe2(2+)Fe2(3+)(PO4)3(OH)3, found in the Yushui Cu deposit, South China. Both of them have the general formula XM12M22(PO4)3(OH)3. Nigelcookite is the first member of the group to have V3+ as the dominant ion at the M2 site, while plumbojohntomaite is the Fe3+-analog of nigelcookite, albeit with V3+ instead of Fe3+. https://doi.org/10.2138/am-2024-9586 Oxybarometry of reduced silicate glasses: Using multivariate methods to constrain Cr oxidation states with application to lunar glasses Molly C. McCanta, M. Darby Dyar, Stephen R. Sutton, Sarah E. Roberts, Cai R. Ytsma Iron valence is generally used to quantify magmatic oxidation state; however, under reducing conditions, such as those of the lunar interior, Fe valence becomes less sensitive to changing redox. McCanta et al. proposed a Cr oxybarometer that may be more sensitive for silicate melts equilibrated at low fO2 (around the iron-wüstite buffer) conditions. https://doi.org/10.2138/am-2024-9602 Sublattice disorder and Fe-Mg substitution in brucite: Implications for the subduction-zone water cycle Weibin Gui, Jin Liu, Ao Deng, Jun Hu, Penghui Sun, Changzeng Fan, Fahui Xiong Gui et al. investigated the structure and properties of brucite, a hydrous mineral that plays an important role in the Earth's water cycle, under high-pressure high-temperature conditions. It is found that the stretching vibrations of hydroxyl groups in brucite change unexpectedly, in association with a second-order phase transition. In Fe-bearing brucite, a secondary vibration band appears due to iron substituting for magnesium in the structure. This vibration band dwindles with increasing pressure but remains at elevated temperatures at 1 bar. Additionally, Fe-bearing brucite decomposes at a lower temperature than pure brucite under oxidizing conditions. These findings provide insight into how brucite contributes to water transport at shallow subduction zones, which is important for understanding the Earth's evolution and habitability. https://doi.org/10.2138/am-2024-9646 Snowball quartz in highly fractionated peraluminous granites: An indicator of multiple magma degassing Daohan Zhang, Kunfeng Qiu, Chang Xu, Yuwei Luan, Yanjun Li, Junhao Wei, Jun Deng Zhang et al. investigated two independent magma chambers that contributed to the formation of the Yashan peraluminous granite pluton. Snowball quartz formed as a result of moderate undercooling (ΔT = 50–100 °C) of the melt during multiple episodes of magma degassing. Multiple magma degassing events facilitate Ta-Nb mineralization during the late evolutionary stage of the Yashan pluton. Snowball quartz can serve as an effective exploration indicator for Ta-Nb deposits associated with highly fractionated peraluminous granites. https://doi.org/10.2138/am-2024-9649 The sulfate-bearing associations of fumarolic environments of Somma-Vesuvius volcano (Italy): A review from historical samples (Royal Mineralogical Museum of Naples) Annamaria Pellino, Angela Altomare, Fabio Bellatreccia, Piergiulio Cappelletti, G. Diego Gatta, Aurelia Falcicchio, Richard Herrington, Nicola Mondillo, Carmela Petti, Concetta Rispoli, Nicola Rotiroti, Mike Ramsey, Mattia Bonazzi, Giuseppina Balassone Pellino et al. investigated sulfate-bearing associations of fumarolic environments of Somma-Vesuvius volcano (southern Italy), reporting new mineralogical data. The study explores these complex associations using various analytical methods, including SEM-EDS, PXRD, SC-XRD, FTIR, and Raman spectroscopy. Sulfates (Cu-, alkali-Cu-, and Pb-bearing sulfates) are the most widespread group, closely followed by halides and then oxides, phosphates, and arsenates, often occurring as rare mineral associations. Unusual phases containing As, Cd, Tl, and N were also identified. This work enhances understanding of genetic environments involving sulfates and can be especially relevant in consideration of the occurrence of sulfates in planetary bodies. https://doi.org/10.2138/am-2024-9666 Fuyuanite [Mg7Nb6O18(OH)8], a new hydrous magnesic-niobic oxide mineral from the Bayan Obo deposit, China Hai-Dong She, Hong-Rui Fan, Yun-Xiang Zhan, Xiang-Ping Gu, Xiao-Chun Li, Kui-Feng Yang, Qi-Wei Wang She et al. described a new magnesic-niobic mineral with hydroxyl from Bayan Obo, China. The mineral's ideal formula is Mg7Nb6O18(OH)8, and it is named fuyuanite. Both the mineral and its name were approved by the IMA-CNMNC (2024-059). https://doi.org/10.2138/am-2024-9676 Olgafrankite, Ni3Ge, a new mineral as the carrier of siderophile germanium in reduced systems Oleg S. Vereshchagin, Maya O. Khmelnitskaya, Albina G. Kopylova, Yulia V. Solov'eva, Maria G. Krzhizhanovskaya, Anatoly V. Kasatkin, Liudmila A. Gorelova, Natalia S. Vlasenko, Sergey N. Britvin Vereshchagin et al. examined samples from the world-famous Norilsk ore region, and found a new mineral, nickel germanide (Ni3Ge), which had previously been found in meteorite material (Rumuruti chondrite, the prototype of the R-type chondrites). The new germanide can be an important germanium carrier in reduced assemblages, in particular in iron- and stony-iron meteorites, where the well-known significant correlations between nickel and germanium may be accounted for by the presence of finely dispersed precipitates of olgafrankite. https://doi.org/10.2138/am-2024-9714 On the labyrinthine crystal-chemistry of boleite, a Pb-Ag-Cu hydroxyhalide G. Diego Gatta, Giorgio Guastella, Pierino Malizia, Tommaso Battiston, Marco Merlini, Geoffrey Bromiley, Oscar Fabelo Gatta et al. investigated the chemical composition and crystal structure of boleite from the Amelia Mine (Boléo District, Mexico) using chemical analytical techniques, single-crystal X-ray, and neutron diffraction. Chemical data show no significant evidence of potential substituents of Pb, Ag, and Cu; the concentrations of REE, PGE, and other industrially relevant elements are insignificant. Despite a lack of crystallographic evidence, chemical data suggest that partial Cl– vs. OH– substitution can occur. The X-ray and neutron diffraction results confirm the previously reported general structural model of boleite but consistently show that a substitutional disorder affects the K site, manifested by a large and unusual displacement parameter. The H-bonding network in the structure of boleite is now unambiguously described on the basis of the neutron structural model. https://doi.org/10.2138/am-2024-9721