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 5; 05-01-2026 Dypingite as a hydration series with reversible change of H2O content Yang Lu, Anton Sednev-Lugovets, Patricia Carvalho, Matylda N. Guzik, Amir Masoud Dayaghi, Kristina G. Dunkel, Håkon Austrheim, Zhiyong Lin, and Henrik Friis Dypingite is a multi-functional mineral. However, its identification has been confused with dypingite-like phases. Lu et al. collected samples from Norway, and, based on structural and compositional results, found that dypingite and dyingite-like phases are a series with different H2O contents. This study draws attention to sample processing on dypingite, consolidates the role of the dypingite series in CO2 sequestration, and gives suggestions for the structure refinement of dypingite. https://doi.org/10.2138/am-2024-9603 Detecting and preserving biosignatures in sulfate minerals prone to instability Karena K. Gill, Kathleen C. Benison, and Elliot A. Jagniecki Hydrated sulfate minerals such as mirabilite (Na2SO4·10H2O) hold significant potential for preserving biosignatures and providing insights into past environmental conditions on Earth and other planetary bodies. However, their instability under most terrestrial conditions presents challenges for laboratory analysis and preservation. This study documents and characterizes primary fluid inclusions in mirabilite from Great Salt Lake, Utah. The diverse biosignatures, including microorganisms and organic compounds, highlight its significance for understanding life in various environments. By employing non-destructive preparation techniques, such as sealing samples in mineral oil or plastic wrap, the stability of mirabilite was extended, enabling advanced analyses using Raman spectroscopy and UV-vis microscopy. These methods preserved key characteristics of the mineral, slowing its rapid dehydration to thenardite (Na2SO4). The findings not only improve the potential for detecting biosignatures in hydrated minerals but also inform strategies for preserving these minerals in geological and astrobiological studies, ensuring the integrity of valuable environmental records. https://doi.org/10.2138/am-2024-9689 Apatite textures, composition, and Sr isotope signatures: Constraints on the genesis of gold at Zaozigou deposit, West Qinling, Central China Germain Kaningu Bishikwabo, Hao-Cheng Yu, Jie Wang, Chao Li, Murat Taner Tamer, Zeng-Sheng Li, Da-Peng Li, Yi-Zhan Sun, Xiao-Gang Luan, Yu-Xi Wang, and Kun-Feng Qiu Apatite is a common accessory phosphate mineral in various hydrothermal ore systems, capable of incorporating a large spectrum of elements. These features make it a good fingerprint of ore formation. In the Zaozigou deposit in Central China, apatite crystals developed within both the ores and barren host rocks; however, the mechanisms of formation have been debated. To address the issue, this study documents the textural, chemical, and Sr isotopic features of multistage apatite. The petrographic evidence reveals four generations of apatite crystals, spanning the magmatic and auriferous metamorphic stages, and characterized by distinct elemental and Sr isotope compositions. The alteration in the elemental and isotopic compositions of apatite is indicative of the pivotal role played by the metasomatic alteration in gold deposition, long after the last stage of magmatism. https://doi.org/10.2138/am-2024-9713 Coupled fluorine and hydroxyl incorporation into forsterite Yaxin Hu, Shun Guo, Joerg Hermann, Nils B. Gies, Di Zhang, and Xiaoguang Li Olivine is a dominant mineral in the Earth's upper mantle and a rock-forming mineral in mafic-ultramafic magmatic rocks and metasomatized dolomitic marbles. Here, we document F-OH-bearing forsterite in dolomitic marbles from the Mogok metamorphic belt (MMB), Myanmar. The MMB forsterite exhibits core-rim zonation of F and OH with higher F (up to 440 μg/g) and H2O (up to 180 μg/g) contents in the rims. Moreover, a positive correlation between F and H2O contents is found. Hu et al. suggest that the clumped fluoride-hydroxyl defects in forsterite at O sites surrounding a Si vacancy lead to a coupled incorporation of F and OH in this mineral. The presence of F thus enhances the incorporation of H2O in olivine. The presence of Si vacancies in olivine leads to a weakening of the mantle. Therefore, mantle metasomatism, for example, by proto-kimberlite melts that introduce F and H2O to the lithospheric mantle, could affect craton stability. https://doi.org/10.2138/am-2025-9762 Goldschmidt’s geochemical classification of the elements: The evolution of a nuanced hypothesis Katharina Lodders and Robert M. Hazen Victor Goldschmidt's influential work on the geochemical classification of the elements is often presented in oversimplified, if not misleading, ways. In the usual telling, each chemical element is assigned to one of four categories based on affinities for the metal, sulfide, oxide, or gaseous phase: siderophile, chalcophile, lithophile, or atmophile, respectively. However, Goldschmidt's evolving presentations of this concept are far more nuanced. In his initial 1923 treatment, he focused on the distribution of elements among the metallic, sulfidic, and silicate phases in meteorites. Accordingly, his division of elements into siderophile, chalcophile, and lithophile elements pertained primarily to the special case of high-temperature, low-pressure environments with coexisting metal, sulfide, and silicate melts. In subsequent publications, Goldschmidt expanded his analytical studies to crustal lithologies, including igneous, sedimentary, and biologically mediated deposits. Under these contrasting environments, an element can adopt varied roles and fall into multiple categories, including a fifth group: biophile. Goldschmidt not only expanded his environment-dependent geochemical classification of the elements, but he also presented a four-part narrative of Earth's "geochemical evolution": a framing that incorporated a prescient description of the co-evolving geosphere and biosphere and anticipated "mineral evolution" by more than half a century. https://doi.org/10.2138/am-2025-9788 Crystal structure evolution of nanohematite during dissolution: Evidence for partitioning of iron vacancies in nanoparticle shells Dong Youn Chung, Peter J. Heaney, Jeffrey E. Post, Joanne E. Stubbs, and Peter J. Eng Nanohematite (Fe2O3) is utilized for the determination of such geochemical soil parameters as oxidation state, pH, and the presence of water (on Earth and Mars), sorption-desorption properties of charged ions in soils, and technological applications, such as the photo-oxidation of water and hydrogen production. Chung et al. explored dissolution mechanisms of nanohematite using time-resolved synchrotron X-ray diffraction (TRXRD), observing that Fe vacancies play a key role in controlling dissolution behavior. Specifically, real-time XRD indicated that Fe occupancies increased during dissolution, and unit-cell parameters increased accordingly. Chen et al. (2023)’s TRXRD study of nanohematite growth showed that Fe occupancy also increases as crystals enlarge. The present study suggests that Fe vacancies in hematite nanoparticles are concentrated in the outer shells relative to the cores. The results also indicates that the structural changes induced by nanoscale sizing are not always reversible as a function of particle size. https://doi.org/10.2138/am-2025-9812 Pressure-induced phase transitions in rhodonite and related chain silicates Wei Zhao, Jingui Xu, Dongzhou Zhang, Qifa Zhong, Shanrong Zhang, Kai Wang, Wenge Zhou, and Dawei Fan This paper presents experimental results on pressure-induced phase transitions in rhodonite (a pyroxenoid) and offers a critical review of such transitions in chain silicates (pyroxenes and pyroxenoids). Pyroxenes and pyroxenoids are significant chain silicates in Earth's crust and mantle. Understanding their high-pressure phase transitions is crucial for elucidating the stability of chain silicates in the deep Earth. Despite extensive research on high-pressure behavior of pyroxenes and existing studies on pyroxenoids, a systematic synthesis comparing the transitions between the two mineral groups has been lacking. Zhao et al. demonstrate that rhodonite undergoes an isosymmetric second-order phase transition at 10.9(1) GPa, driven primarily by increased Mn coordination number. The work emphasizes the critical roles of SiO4 tetrahedral rotations and coordination number increases, and their interplay in governing phase transitions. https://doi.org/10.2138/am-2025-9856 Behavior of thallium during subduction-zone devolatilization in the Western Alps HP/UHP metasedimentary rocks: The role of phengite J. Cameron Adams, Shelby T. Rader, Richard M. Gaschnig, and Gray E. Bebout The Schistes Lustrés and Lago di Cignana samples examined here represent HP/UHP metamorphic conditions with an accompanying ~20% loss of H2O during devolatilization, coinciding with a change in relative mineral abundance. Adams et al. show, through trace element data and Tl isotopic compositions, that phengite dominates the Tl (and LILE) budget, serving as the primary mineralogical reservoir at depth, and affects fluid-mineral partitioning during devolatilization. This highlights the importance of phengite in potentially modulating arc rock trace element signatures after subduction. https://doi.org/10.2138/am-2025-9864 Incommensurately modulated high-pressure modification of K-cymrite: Role of guest H2O molecules Alexandr V. Romanenko, Sergey V. Rashchenko, and Andrey V. Korsakov In this study, Romanenko et al. investigated the incommensurate modulated high-pressure modification of K-cymrite (KAlSi3O8 · H2O) through in situ single-crystal synchrotron X-ray diffraction. This research contributes to the understanding of the structural properties of K-cymrite under extreme conditions, shedding light on its behavior in natural geological environments and its potential applications as a water and large-ion lithophile element transporter into the mantle. The data presented in this article are crucial for thermodynamic modeling of the composition of fluid-saturated crust. https://doi.org/10.2138/am-2025-9865 Wenqingite, Pb5(AsS3)2(Ge2S6), the first thiogermanate and thioarsenite mineral with edge-sharing GeS4 tetrahedra, from the Wusihe Pb-Zn deposit, Sichuan Province, SW China Yu-Miao Meng, Ruizhong Hu, Xiao-Wen Huang, Yiping Yang, Guanghua Liu, and Xiangping Gu Wenqingite is the first thiogermanate-thioarsenite mineral of economic significance, discovered in the Wusihe Pb-Zn deposit, SW China. It is closely associated with galena, pyrite, jordanite, and ruizhongite within a sphalerite matrix. The discovery of wenqingite, along with ruizhongite in the same deposit, updates the knowledge that Ge is mainly present in sphalerite. The occurrence of Ge minerals with different compositions provides new insights into Ge enrichment in sulfide deposits. https://doi.org/10.2138/am-2025-9872 Crystal chemistry and phase stability of wuyanzhiite, a new mineral dimorphous with chalcocite, from the Bofang Copper Mine, Hunan, China Xiangping Gu, Xiangyang Shi, Hexiong Yang, and Guanghua Liu The Cu-S system contains a complex suite of minerals and synthetic phases with various Cu/S ratios. They are not only important ore minerals, but also have great potential applications in ion conductors, solar cell absorbers, and even Cu-doped superconductors. The tetragonal phase of Cu2S has attracted attention from geological and material sciences for its better stability in high temperatures and pressures. This paper presents a detailed description of the new mineral wuyanzhiite approved by IMA-CNMNC (IMA2017-081), including: (1) the first structure determination of natural tetragonal Cu2S from single-crystal diffraction; (2) new data on its chemical composition indicate a wide range of cation/S ratios from 1.993 to 1.710, Fe content from 0 to 2.88 wt% (0–0.074 apfu), and close correlations between Cu/S ratio, Cu1+, Cu2+, and Fe; (3) new data on its stability at ambient conditions indicate that the high contents of Fe (>0.7 wt%) may enable the stability of the phase over 13 years. https://doi.org/10.2138/am-2025-9910 Framework response to local order in hollandite Marta Morana, Ella M. Schmidt, Cristian Biagioni, Alexei Bosak, and Giovanni O. Lepore Combining X-ray diffuse scattering and X-ray absorption spectroscopy provides a comprehensive view of hollandite's [Ba(Mn4+6Mn3+2)O16] local structure. Barium atoms show local correlations between adjacent tunnels, and the octahedral Mn framework shows a structural response to the presence of the channel cations. https://doi.org/10.2138/am-2025-9916 Mampsisite, Ca4Al2(OH)12(CO3)·5H2O, a new mineral and a new polymorph of the cementitious AFm monocarboaluminate Sergey N. Britvin, Michail N. Murashko, Natalia S. Vlasenko, Oleg S. Vereshchagin, Vladimir N. Bocharov, and Yevgeny Vapnik This article reports a discovery of Ca-Al layered double hydroxide mineral, the first purely carbonate member of the hydrocalumite group, a new structural type of a cementitious AFm calcium monocarboaluminate phase. The close similarity between the basal interlayer spacing of mampsisite and synthetic AFm monocarboaluminate and to basal spacings of 2:1 layered double hydroxides (e.g., quintinite group) suggests that mampsisite may be easily missed during powder XRD analysis of cementitious materials and natural Ca-bearing clays. https://doi.org/10.2138/am-2025-9950