American Mineralogist June 2026 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 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 6; 06-01-2026 Grahampearsonite, Ca2P2O7, a new mineral found in a super-deep diamond from Juína, Brazil Yanjuan Wang, Fabrizio Nestola, Maxwell C. Day, Tiago Jalowitzki, Eduardo Novais Rodrigues, Fernanda Gervasoni, Daniel Grings Cedeño, Sebastião William Da Silva, Reinhardt Adolfo Fuck, Jacopo Nava, Lisa Santello, Martha G. Pamato, Davide Novella, Francesca Innocenzi, Andrea Curtolo, Mattia La Fortezza, Kai Qu A new mineral with the chemical formula Ca2P2O7, named grahampearsonite, was found within a super-deep diamond (a diamond that forms at a depth of at least 300 km in the Earth's mantle) from Brazil. The new mineral honors Dr. Graham Pearson from the University of Alberta and was approved as a new mineral by IMA with number 2025-017. The occurrence of grahampearsonite in a super-deep diamond may provide new insights into the Earth's deep phosphorus reservoir and the crust-mantle phosphorus cycle. https://doi.org/10.2138/am-2025-10072 Spatial trace element variations of stibnite in a world-class Sb deposit and their implications for ore genesis and exploration Degao Zhai, Anthony E. Williams-Jones, Qingqing Zhao, Jinchao Wu, Jiajun Liu, Junwei Xu Zhai et al. studied stibnite samples collected from a variety of depths in a world-class Sb deposit to determine their trace element signatures and identify features of these signatures that could be used in the exploration for similar deposits elsewhere. Furthermore, the authors compiled published data on the trace element compositions of stibnite for various ore deposits worldwide, discovering that their trace elements can be used to distinguish distinct metal associations in natural hydrothermal ore systems. This further provides implications for using stibnite trace elements to determine metal associations and the genesis of Sb-bearing mineralization. https://doi.org/10.2138/am-2025-9749 Apatite from metaluminous to peralkaline high-silica rhyolites in Yunshan Caldera (SE China): Implications for the evolution of magmatic systems Wentao Hong, Xisheng Xu, Kai Zhao, Pingli Chu, Dongbo Tan, Shaogang Wei, Rui Shi This study examines apatite in zircons and the volcanic matrix of high-silica rhyolites in the Yunshan Caldera, SE China, to track magma evolution. Apatite inclusions in zircon record heterogeneous crystal mush conditions, whereas apatite microphenocrysts reflect erupted magmas. Their distinct geochemistry captures melt accumulation and homogenization, generating eruptible rhyolites. However, apatite inclusions may not always represent erupted magma compositions, limiting their use in detrital zircon studies. https://doi.org/10.2138/am-2025-9823 Experimental hydrogenation of pure and Cr-doped rutile at variable temperature, pressure, and oxygen fugacity Mona Lueder, Jörg Hermann, Paolo A. Sossi Lueder et al. studied the solubility of hydrogen in rutile with different trace-element compositions and thus different defect chemistries. Hydrogen contents in experimental run products vary between 60 and 500 µg/g, increasing with pressure and oxygen vacancy concentration and decreasing with oxygen fugacity. Comparing experimental results with natural data, the authors identified evidence for hydrogen retention in natural rutile up to ~650 °C. Thus, hydrogen is retained to much higher temperatures than has been suggested by studies on hydrogen diffusion in rutile. https://doi.org/10.2138/am-2025-9852 From hydroxylbastnäsite to bastnäsite: A crystal chemistry perspective of the incomplete solid solution Qifa Zhong, Jingui Xu, Wei Zhao, Dongzhou Zhang, Shanrong Zhang, Kai Wang, Bin Fu, Wenge Zhou, Dawei Fan This is the first study to reveal: (1) the positions of hydrogen atoms in bastnäsite and hydroxylbastnäsite, as well as the order-disorder transition of hydrogen initiated by F-OH substitution in hydroxylbastnäsite, which explains the discrepancies in Raman spectroscopy between synthetic end-members and natural hydroxylbastnäsite; (2) the phase boundary between bastnäsite and hydroxylbastnäsite, with crystal structural data indicating a phase boundary at F = 0.41-0.52 apfu; and (3) the effect of F-OH substitution on the volume of the Bsn-Ce–Hbsn-Ce solid solution. This study is also the first attempt to establish a quantitative framework for describing the volume-composition behavior of incomplete solid solutions involving F-OH substitution. https://doi.org/10.2138/am-2025-9859 Formation pathways of Zn-spinel nanoparticles in Zn-contaminated soils and sediments Michael Schindler, Tessa Warkentine, Xinyang Li Schindler et al. investigated abiotic pathways of zinc (Zn)-spinel formation at low temperatures in Zn-contaminated soils and sediments. Spinels commonly form in these environments as nanomaterials in porous organic matter and on surfaces of clay minerals and Fe-(hydr)oxides. TEM shows that franklinite formation in organic matter is often coupled to weathering of primary Zn-oxide and -sulfide phases emitted by a local smelter or released during mining activities. On the contrary, the formation of Zn-bearing magnetite on clay minerals is decoupled from the weathering process. It occurs primarily via the heterogeneous nucleation on the hydrophilic edges of their basal surfaces. This work suggests that sequestration of contaminants such as Zn via the formation of low-temperature spinels occurs more often than previously assumed. https://doi.org/10.2138/am-2025-9873 Super-hydrous arc magmas delay magnetite saturation and sulfide precipitation Lanqin Li, Xingcheng Liu, Jintuan Wang, Zhongxing Sun, Xiaolin Xiong This study reveals that high water in arc magmas (“super-hydrous” conditions) significantly delays the formation of key minerals: magnetite (iron oxide) and sulfides. This keeps iron and valuable ore-forming metals (such as copper and gold) dissolved in magma for longer, profoundly influencing how and where mineral deposits form. This is crucial for understanding Earth's metal distribution and for guiding mineral exploration. https://doi.org/10.2138/am-2025-9896 Hydrothermal rutile as a recorder of fluid evolution and W mineralization: Insights from the Northern Baoshan Block, China Xiaobo Si, Xiang Sun, Ke Xiao, Qiang Li, Xu Zheng, Ke Miao, Yaqi Ye The Wuchashu cassiterite and Shiganghe rutile yield U-Pb ages of 70.2 ± 2.1 Ma and 73.0 ± 5.5 Ma, respectively, indicating coeval W-Sn mineralization from the same magmatic-hydrothermal event. The Wuchashu rutile formed from ilmenite replacement driven by late-stage hydrothermal fluids, and the Shiganghe rutile crystallized directly from hydrothermal fluids and subsequently underwent alteration. The trace elements (e.g., Zr, Nb, Fe, Cr, V, Sb) in hydrothermal rutile can reveal variations in the physicochemical conditions (e.g., temperature and oxygen fugacity) of ore-forming fluids associated with W-Sn mineralization. Rutile can serve as an effective carrier for W, preventing its loss in F- and B-rich magmatic-hydrothermal systems and releasing W through a decrease in oxygen fugacity and alteration by late-stage fluids, thereby promoting W mineralization. https://doi.org/10.2138/am-2025-9914 Most nakhlite martian meteorites were magmas, not crystal cumulates Allan H. Treiman Most nakhlite martian meteorites retain the compositions of their original magmas and are not accumulations of augite crystals. This recognition, that Mars produced pyroxenitic magma, means that Mars' mantle contains significant proportions of pyroxenite (at least locally), in addition to the expected peridotite. So, the martian mantle is more complex than previously thought, and models of martian magmatism must include contributions from mantle pyroxenite. https://doi.org/10.2138/am-2025-9919 The bond-valence topological model I: The bond-valence topological map of tourmaline from Forshammar, Sweden Peter Bačík This publication develops the application of Bond Valence Topological Modeling to solve crystal-chemical problems and is the first attempt to model the structure of a real sample based on theoretical structural arrangements. The functional Bond Valence Topological Modeling, the connection of Structural Topology and Bond Valence Theory, can be used to reveal processes occurring at the deepest atomic-to-subatomic level that are involved in the crystallization of minerals. https://doi.org/10.2138/am-2025-9920 Thermodynamic and elastic properties of uvarovite at mantle conditions: Insights from first-principles calculations Xu Zheng, Yi Wang, Jiajun Jiang, Feiwu Zhang First-principles simulations reveal the thermodynamic and elastic properties of uvarovite under extreme high-pressure and high-temperature conditions. The model suggests that uvarovite is present at depths of approximately 50-250 km in the subcontinental lithospheric mantle (SCLM) across different SCLM types (Archon, Proton, and Tecton) along a typical geotherm. The transition from Archon to Tecton results in a notable increase in density, which could act as a catalyst for delamination and other dynamic processes influencing mantle convection. By simulating the density and wave velocities of a peridotitic mantle mixture with varying uvarovite content at depths from 400 to 660 km, Zheng et al. demonstrate that a modest addition (~20 vol%) of uvarovite at 660 km depth enhances density by approximately 4%, while slightly reducing both P- and S-wave velocities (~2-3%). These findings suggest uvarovite-rich regions may contribute to the formation of small-scale, low-velocity, high-density zones in the upper mantle and transition zone, which are relevant to seismic heterogeneities observed in these regions. https://doi.org/10.2138/am-2025-9947 Characterization and classification of unregulated mineral fibers: The case of fibrous datolite from Rio Manubiola Valley, Parma, Italy Riccardo Fantini, Rossella Arletti, Francesco Colombo, Giorgia Confalonieri, Tommaso Giovanardi, Magdalena Lassinantti Gualtieri, Daniele Malferrari, Maurizio Scacchetti, Alessandro F. Gualtieri This study provides the first crystal-chemical and toxicological investigation of a fibrous datolite. Despite respirable dimensions according to World Health Organization 1997 Directives, the analysis indicates negligible toxicity and no carcinogenic potential. These results are not only reassuring, given the growing industrial importance of boron minerals, but also position fibrous datolite as a negative control candidate in toxicity studies and support its exclusion from regulatory concerns. https://doi.org/10.2138/am-2025-9988 Karlditmarite, Cu9O4(PO4)2(SO4)2, the first copper phosphate-sulfate mineral from the Tolbachik volcano, Kamchatka, Russia Oleg I. Siidra, Evgeny V. Nazarchuk, Leonid A. Pautov, Artem S. Borisov, Anatoly N. Zaitsev, Evgeniya Yu. Avdontseva Karlditmarite is the first Cu phosphate-sulfate mineral among more than 100 various copper oxysalts known from the active fumaroles. The crystal structure of karlditmarite contains tetrahedral copper-oxide layer of unique topology. Fumarolic minerals that contain similar complexes are an exceptional source of inspiration and playground for the investigation of intricate magnetic phenomena. https://doi.org/10.2138/am-2025-9994 ------------------------- American Mineralogist Mineralogical Society of America (MSA) Chantilly, VA 20151 editorial@minsocam.org<mailto:editorial@minsocam.org> Website: https://msaweb.org/MSA/AmMin/