American Mineralogist September 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 9; 09-01-2025 Thorite: An oddity in phase stability among the zircon-structured orthosilicates at high pressures Andrew C. Strzelecki, Jason L. Baker, Stella Chariton, Xiaodong Zhao, Vitali Prakapenka, David Bollinger, Sohan Ahmed, Jeffrey Fortner, Stephanie Szenknect, Adel Mesbah, John S. McCloy, Choong-Shik Yoo, Rodney C. Ewing, Nicolas Dacheux, Hongwu Xu, Xiaofeng Guo Strzelecki et al. report a complete study of the thorite-to-huttonite transition under high pressure, with equations of state and bulk moduli derived for these two phases. The authors propose a new pressure-temperature phase diagram for ThSiO4 with an update for the boundary of the thorite-to-huttonite transition. As a result, the enthalpy of formation of huttonite, based on the Clapeyron equation, was found to be close to 0 kJ/mol, which suggests its metastability (and hence rarity) in natural systems. https://doi.org/10.2138/am-2024-9443 High P-T single-crystal elasticity of zircon by Brillouin spectroscopy Arlacee Luu, Wen-Yi Zhou, Xin Zhong, Ming Hao, Przemyslaw Dera, Jin S. Zhang Luu et al. performed high P-T single-crystal elasticity measurements of zircon using Brillouin spectroscopy at pressures up to 7 GPa and temperatures up to 700 K. The data have a high signal-to-noise ratio and provide the first high P-T single-crystal elasticity model of zircon. The study utilized the high P-T single-crystal elasticity data of zircon and garnet to evaluate the potential applications of zircon-garnet in elastic thermobarometry via elastic modelling. High incompressibility and stiffness over a range of T suggest zircon could be ideal to estimate entrapment conditions. https://doi.org/10.2138/am-2024-9458 Germanium oxidation state and substitution mechanism in Ge-rich sphalerite from MVT deposits: Constraints from X-ray absorption fine structure (XAFS) and geometric optimization Pan-Pan Niu, Shao-Yong Jiang, Manuel Muñoz, Clément Bonnet, Olivier Mathon, Marie-Christine Boiron, Hai-Zhen Wei, Suo-Fei Xiong Germanium is an abundant critical metal in sphalerite, especially in MVT Pb-Zn deposits. However, the distribution of Ge oxidation states in sphalerite remains unclear, and there is a lack of crystal structure information regarding the Ge substitution mechanisms into sphalerite. Based on synchrotron XAFS, we have observed that Ge4+ predominates when coupled with Cu, demonstrating a more ordered and stable structure. Conversely, when coupled by vacancy, a small amount of Ge2+ emerges, and the whole structure shows a significant disorder. The widespread Cu-Ge coupling mechanisms suggest that Cu plays a crucial role in facilitating the enrichment of Ge within sphalerite. The determination of the Ge oxidation state provides an important reference to infer the Ge substitution mechanism in sphalerite through elemental correlations. This study has modified the widely accepted Ge-vacancy coupling mechanism and confirmed that As enters the sphalerite lattice rather than being in nano-mineral Cu-S-As inclusions evenly distributed within sphalerite. https://doi.org/10.2138/am-2024-9485 Berndlehmannite: A new V-bearing sulfide mineral from the black-shale-hosted Zhongcun vanadium deposit, South China Xuerui Fu, Guowu Li, Lingang Xu, Yuan Xue, Ningyue Sun, Jinhua Hao, Wei Jian, Hao Yan, Huishou Ye, Jianhua Ding, Peng Yuan The new V-bearing sulfide mineral, berndlehmannite, was discovered in the black-shale-hosted Zhongcun vanadium deposit, South China. Berndlehmannite is a member of the carrollite subgroup within the spinel group. The ideal empirical formula of berndlehmannite is Cu(Cr,V)S6, and it has the highest component of V among the V-bearing minerals in black shales. The discovery of berndlehmannite potentially unveils a previously unrecognized hyper-enrichment process of vanadium in black shales, which requires further study. https://doi.org/10.2138/am-2024-9541 In situ Raman spectroscopic investigation on the phase transition of grunerite at high pressures Zhi Zheng, Shaohao Zou, Chuanjun Wu, Shenghua Mei In this study, Zheng et al. studied the phase transitions of grunerite at pressure up to ~23.66 GPa using a diamond anvil cell combined with in situ Raman spectroscopy. The study demonstrated the mode splits of the OH vibration modes with increasing pressure, corresponding to a C2/m-to-P21/m phase transition. The splitting of the OH stretching modes resulted from the distinct environments of two OH positions in the P21/m phase, in comparison to the crystallographically identical OH positions in the C2/m phase. The use of Raman spectroscopy, as presented, offers a quick and accessible analytical method for studying phase transitions in grunerite samples, with potential applications for other minerals within the amphibole group. https://doi.org/10.2138/am-2024-9560 Reconstructing volatile evolution in melts using zircon-hosted apatite inclusions: Implications for the use of apatite as a fertility indicator Qiang Li, Xiang Sun, Jun Deng, Yunzhao Ge, Xiaobo Si, Xu Zheng, Pete Hollings The cathodoluminescence and chemical composition of apatite, particularly the Mn/Fe ratio and REE content, can effectively discriminate between primary magmatic apatite and hydrothermally altered apatite. Apatite-in-zircon is of superior value for reconstructing melt volatile evolution and could be a better Cu-fertility indicator than apatite inclusions hosted by other silicate minerals (e.g., amphibole, biotite, plagioclase, and quartz). Interpreted primary magmatic Cl contents are high in post-subduction porphyry Cu deposit and would effectively extract copper from melt to hydrothermal fluid during volatile exsolution in the magma chamber. https://doi.org/10.2138/am-2024-9561 Silicate liquid immiscibility in the Chang'e 5 lunar mare magmas: Constraints on the petrogenesis of lunar granitic rocks Le Zhang, Ya-Nan Yang, Jintuan Wang, Ze-Xian Cui, Cheng-Yuan Wang, Peng-Li He, Yan-Qiang Zhang, Mang Lin, Yi-Gang Xu Silicon-rich melt inclusions hosted in fayalite fragments from Chang'e 5 lunar soil formed through late-stage silicate liquid immiscibility in lunar mare basaltic magmas. Their major and trace elemental compositions are similar to those of lunar granitic rocks. The results of this study support the possibility that lunar granitic rocks formed through silicate liquid immiscibility. https://doi.org/10.2138/am-2024-9577 Formation and transformation of clay minerals in Mars-analog rock varnish Qian Fang, Yan Li, Hongrui Ding, Liao Yang, Hanlie Hong, Zhong-Qiang Chen, Anbei Deng, Qile Geng, Anhuai Lu Fang et al. examined clay minerals in rock varnish distributed across different climatic zones in China. Rock varnish is considered a representative analog for studying traces of life and water-rock interactions on Mars. The study found that the composition and crystallinity of clay minerals in rock varnish correlate with climatic background. Fang et al. found that illite exists in both detrital and authigenic forms, and it can transform into chlorite, a transformation typically reported in metamorphic conditions. https://doi.org/10.2138/am-2024-9585 Lianbinite, (NH4)(C2H3O3)(C2H4O3), a new glycolate mineral, from the Santa Catalina Mountains, Tucson, Arizona, U.S.A. Hexiong Yang, Xiangping Gu, Warren Lazar, Ronald B. Gibbs, Robert T. Downs A new organic mineral species, lianbinite was discovered from the western end of Pusch Ridge in the Santa Catalina Mountains, north of Tucson, Arizona, U.S.A. Lianbinite is colorless and transparent, with a white streak, vitreous luster, low Mohs hardness (1–1 1/2), and perfect {100} cleavage. The crystal structure of lianbinite contains two forms of glycolate units: glycolate anions (GAs) and glycolic acid molecules (GMs), which alternate along [010] and are linked together by strong H-bonds to form chains. The discovery of lianbinite, together with other glycolate minerals documented thus far, namely lazaraskeite, stanevansite, domitrovicite, jimkrieghite, rasmussenite, and glecklerite, implies that glycolate minerals may be widespread in nature, thus serving as a potential reservoir for biologically fixed carbon. https://doi.org/10.2138/am-2024-9587 Vesuvianite as a key tool for the reconstruction of skarn formation conditions: An example from the Sauce Chico Complex, Argentina Carlos A. Ballivián Justiniano, Maricel G. Rodríguez, Taras L. Panikorovskii, Manuela E. Benítez, Clemente Recio, Cinthia P. Ramos, Mabel E. Lanfranchini, Florencia Di Salvo The elasticity of the vesuvianite structure allows its chemical complexity and adaptation capability under different crystallization conditions, making it a useful mineral in the reconstruction of skarn formation conditions. The Loma Marcelo skarn is the result of superimposed processes related to the intrusion of an Ediacaran granite and the contribution of temperature and fluids related first to an alkaline early Cambrian magmatism and then to a Permian tectono-metamorphic event. The Loma Marcelo skarn vesuvianite reflects a retrograde process related to the Ediacaran magmatism. Despite subsequent events, the vesuvianite studied does not seem to undergo important structural modifications. That is, the vesuvianite structure is fixed at the time of its formation and does not change during later processes. This suggests that vesuvianite-group minerals have the potential to be a robust XRD-based thermometer as proposed by Panikorovskii et al. (2023), which does not undergo subsequent modifications, unlike, for example, stable isotope thermometers that require the isotopic equilibrium or fluid inclusions. https://doi.org/10.2138/am-2024-9588 The high-pressure, vacancy-stabilized component in clinopyroxenes Ioannis Baziotis, Chi Ma, Stephan Klemme, Jasper Berndt, Oliver Tschauner, Paul D. Asimow Motivated by the recent discovery of albitic clinopyroxene, Baziotis et al. assess the molar volume of vacancy-rich, high-pressure clinopyroxenes. The authors compiled a series of data (including this study) and created a model for volumes of clinopyroxenes in a multi-component subsystem, showing that the symmetric excess volume model is the most appropriate way to fit the data. The proposed volume model provides a partial basis for assessing the formation conditions of vacancy-stabilized pyroxenes. https://doi.org/10.2138/am-2024-9609 Mariakrite, [Ca4Al2(OH)12(H2O)4][Fe2S4]: A new mineral and the first layered double hydroxide intercalated with dithioferrate (iron disulfide) chains Mikhail N. Murashko, Yevgeny Vapnik, Natalia S. Vlasenko, Oleg S. Vereshchagin, Yulia S. Shelukhina, Igor V. Pekov, Sergey N. Britvin This study reports the first representative of natural layered double hydroxides (LDH) with dithioferrate, [FeS2]– in the role of an interlayer anion, from pyrometamorphic rocks in the Negev Desert. The new mineral, mariakrite, is the first cementitious layered Ca-aluminate (AFm phase) intercalated with sulfide anion, and the first sulfide-bearing LDH with a completely solved crystal structure. Mariakrite is a unique example of dithioferrate in which disulfide chains have no contact with cations or anions, being suspended between hydroxide layers via the system of H-bonds. Consequently, the mineral might represent the near-ideal model for studying intricate physical properties of isolated quasi-one-dimensional dithioferrate chains. The chemical composition of mariakrite allows this mineral to be proposed as a single-phase precursor to forming meteoritic Ca-Fe oxysulfides in thermally metamorphosed carbonaceous chondrites of the CY group and their asteroid parent bodies. https://doi.org/10.2138/am-2024-9624 Enrichment mechanism of heavy rare earth elements in magmatic-hydrothermal titanite: Insights from SXAS/XPS experiments and first-principles calculations and implications for regolith-hosted HREE deposits Yuzhou Feng, Huayong Chen, Huiyao Kuang, Rucao Li, Bing Xiao, Chao Wu, Hui Zheng, Renfei Feng, Mohsen Shakouri, Yuanming Pan This study investigated two texturally distinct types of HREE-enriched titanite (titanite I and II) in granites from the Gucheng regolith-hosted HREE deposit in South China. The samples have different Y, HREE-O first shells, suggesting that Y3+ (and HREE3+) occupy the 7-coordinated Ca site via three substitutions, detailed by Feng et al. These findings support that the crystallization of HREE-enriched titanite in granites plays an important role in forming HREE-dominated regolith-hosted deposits. https://doi.org/10.2138/am-2024-9645