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 The olivine-spinel-a(melt/SiO2) (OSaS) oxybarometer: A new method for evaluating magmatic oxygen fugacity in olivine-phyric basalts Aaron S. Bell, Laura E. Waters, and Mark Ghiorso https://doi.org/10.2138/am-2023-9021 This paper describes the calibration and implementation of a new method for conducting magmatic f(O2) studies. The new approach, based on olivine-spinel-melt equilibrium, only requires access to an electron microprobe and the identification of cotectic olivine and spinel pairs in mafic rocks. The new oxybarometer generates f(O2) values with comparable accuracy to magmatic redox studies that use XANES or Mössbauer measurements of Fe2+/Fe3+ in quenched glasses. Arsenic in pyrite acts as a catalyst for dissolution-reprecipitation reaction and gold remobilization Dennis Sugiono, Laure Martin, Nicolas Thébaud, Denis Fougerouse, Crystal K. LaFlamme, Marco Fiorentini, Laura Petrella, Paul Guagliardo, Steve Reddy, Si-Yu Hu, and Alexandra Suvorova https://doi.org/10.2138/am-2023-9034 This manuscript presents evidence of a direct link between low-angle boundaries between chemically distinct zones in pyrite and the distribution of native gold and arsenopyrite. The link between these boundaries and Au occurrence (disseminated and free native grains) in pyrite demonstrates that As and Au within the pyrite lattice are sensitive to permeation of hydrothermal fluids along low-angle boundaries. Coupled dissolution-reprecipitation of pyrite along the low-angle boundaries creates native gold in an As-depleted domain. Miyake-jima anorthite: A lunar crustal material analog Arkadeep Roy, Ananya Mallik, Kerri Donaldson Hanna, Tyler J. Goepfert, and Richard L. Hervig https://doi.org/10.2138/am-2023-9122-a Here, we report the major and trace elements along with infrared spectra of high calcium plagioclase grains from Miyake Island in Japan. The grains have compositional and spectral similarities to plagioclase from primary lunar highland crustal suites. We demonstrate the suitability of the Miyake Island plagioclase samples as excellent material analogs and also standard material for future studies on the geochemistry, experimental petrology, geophysics, and remote sensing of the lunar crust. In-situ and ex-situ experimental investigation on the chalcopyrite replacement in saline solution at 310–365 °C and 15–25 MPa Luying Wang, Heping Li, Qingyou Liu, Sen Lin, and Shengbin Li https://doi.org/10.2138/am-2023-9136 The effects of temperature (310 to 365 °C) and pressure (15 to 25 MPa) on chalcopyrite replacement in NaCl solutions were investigated by combining ex situ surface characterization and in situ electrochemical techniques. Elevated temperature and pressure promote chalcopyrite dissolution by different oxidative pathways. At elevated temperature, copper ions are preferentially released from the chalcopyrite surface, resulting in further dissolution with less covellite and more hematite forming on the chalcopyrite surface. At elevated pressure, more iron ions diffuse through the passive covellite layer by point defects, favorably promoting chalcopyrite replacement by covellite. The pathway of chalcopyrite replacement can be applied in the hydrothermal brine-chalcopyrite reactions of the copper deposits, where covellite surrounds chalcopyrite and Fe oxides coexist with chalcopyrite, to explain the exchange of Fe/Cu ions between chalcopyrite and solution. Cassiterite and Sn mineralization in the giant Bayan Obo Fe-Nb-REE deposit, Northern China Ya-Ting Xu, Ru-Cheng Wang, Mei-Fu Zhou, and Fu-Yuan Wu https://doi.org/10.2138/am-2023-9149 Xu et al. report extremely high Sn contents (up to 1500 ppm Sn) in the Bayan Obo, the world's largest REE deposit. The authors identified abundant cassiterite in the forms of nanoscale grains in magnetite and late granular grains in massive REE-Fe ores. These indicate that the Bayan Obo deposit has significant Sn mineralization in addition to vast amounts of REE and Nb. Multiple high-precision geochronological analyses on ore minerals (columbite, monazite, and parisite) coexisting with cassiterite reveal two separate stages of mineralization and confirm the co-generation of tin (Sn) and niobium (Nb) in the Bayan Obo deposit. The results support a possible model for Sn mineralization: Sn genetically originated from carbonatite magma, and the main early stage of Sn mineralization is coeval with massive magnetite mineralization. Subsequently, Early Paleozoic hydrothermal events facilitated the remobilization and further enrichment of Sn. Mushroom-shaped growth of crystals on the Moon Jiaxin Xi, Yiping Yang, Hongping He, Haiyang Xian, Shan Li, Xiaoju Lin, Jianxi Zhu, and H. Henry Teng https://doi.org/10.2138/am-2023-9214 Xi et al. report a novel mineral assemblage found in a lunar breccia clast recently returned by CNSA's Chang'e-5 mission. A careful characterization of the mineral samples revealed the presence of parallel olivine rods with a stripe-like pattern intricately entangled with nanospheres of troilite and metallic iron (npFe0). Based on the geometry and element depletions, olivine associated with troilite was likely the Cr source, and adjoining impact glass was the Fe source for chromite crystallization. Such process and the resultant structure have never been reported in Earth samples, though homogeneous whiskers and dendrites of mantle-derived minerals (e.g., pyroxene and olivine) are common in some volcanic glasses. Considering the frequent (micro)meteoroid impacts on the Moon, the conditions to form aggregates such as these may be very common in lunar regolith, significantly shaping the mineral composition and the geological evolution of the lunar surface. In addition, similar crystallization pathways may also occur in mantle-derived materials under conditions sufficiently far from equilibrium. Enrichment and fractionation of rare earth elements (REEs) in ion-adsorption-type REE deposits: Constraints of an iron (hydr)oxide-clay mineral composite Xiaoliang Liang, Puqiu Wu, Gaoling Wei, Yiping Yang, Shichao Ji, Lingya Ma, Jingwen Zhou, Wei Tan, Jianxi Zhu, and Yoshio Takahashi https://doi.org/10.2138/am-2023-9217 Ion-adsorption-type rare earth element (REE) deposits are the source of more than 90% of global heavy REEs (HREEs). Thus, understanding the ore genesis of REEs, particularly the distribution characteristics and enrichment mechanisms of HREEs, is vital for efficient exploration and mining of ion-adsorption-type REE deposits worldwide. The characteristics and petrogenesis of bedrock and the aqueous mobility of REEs are important factors controlling REE accumulation and fractionation in the weathering crust of REE deposits. Since the effect of REE adsorption on secondary minerals, a crucial step in deposit formation, remains poorly understood, Liang et al. investigated the enrichment and fractionation of REEs relative to interface reaction on relevant clay minerals. Composites of ferrihydrite-kaolinite, goethite-kaolinite/halloysite, and hematite-kaolinite/halloysite were found to be distributed in the semi-weathered, completely weathered, and topsoil layers, respectively, with different sizes and shapes. Ion-exchangeable-REEs on clay minerals were enriched in the upper completely weathered layer. Fe (hydr)oxides scavenge REEs through complexation and oxidation, resulting in HREE enrichment and a positive cerium (Ce) anomaly. Compared with crystalline Fe (hydr)oxides, amorphous Fe (hydr)oxides immobilize more REEs but exhibit weaker preferential adsorption of HREEs. Furthermore, the distributions and stabilities of light REEs and HREEs were distinguished through simulated adsorption experiments and TEM energy-dispersive spectroscopy analyses. Mineral precipitation sequence from multi-stage fluids released by eclogite during high-pressure metamorphism Ting-Nan Gong, Jin-Xue Du, Li-Fei Zhang, Zhen-Yu Chen, Ze-Ming Zhang, Wei-(RZ) Wang, and Yuan-Ru Qu https://doi.org/10.2138/am-2023-9218 Detailed petrological and phase equilibria modeling reveal an omphacite vein formed during deep subduction and early exhumation stages in southwestern Tianshan in China. The omphacite-rich vein has a mineral assemblage similar to that of the host eclogite. Precipitation sequences of vein minerals reveal the nature and evolution of multi-stage fluids. High-pressure fluids released by lawsonite breakdown during early exhumation can potentially modify the chemical compositions of arc magmas. Plastic deformation of dry, fine-grained olivine aggregates under high pressures Reynold E. Silber, Jennifer Girard, Haiyan Chen, and Shun-ichiro Karato https://doi.org/10.2138/am-2023-9223 Dynamics in the Earth's upper mantle mineral assemblages are sensitive to pressure. For example, pressure strongly modulates deformation by dislocation creep in the upper mantle. However, the diffusion creep dependence on pressure in the upper mantle is not well constrained. To investigate the effect of pressure on diffusion creep, ultrafine-grained synthetic and natural olivine were deformed at conditions corresponding to the upper mantle. The study was conducted at the Advanced Photon Source at the Argonne National Laboratory using a D-DIA apparatus. The results show that the pressure effect, generally expressed through the value of activation volume in the diffusion creep equation, is small relative to dislocation creep. The measured activation volume for diffusion creep in dry synthetic and natural ultrafine-grained olivine samples is V*= 7 ± 2.4 cm3/mol. This study also shows that water has a moderate effect on enhancing diffusion creep in the upper mantle. Estimating modal mineralogy using Raman spectroscopy: Multivariate analysis models and Raman cross-section proxies Laura B. Breitenfeld, M. Darby Dyar, Timothy D. Glotch, A. Deanne Rogers, and Miriam Eleazer https://doi.org/10.2138/am-2023-9224 This work provides fundamental groundwork for using Raman spectroscopy to quantify modal mineralogy. Two techniques are presented in this work for quantifying common rock-forming minerals: partial least-squares multivariate analysis and a novel approach called Raman cross-section proxies (numerical metrics associated with specific Raman features). Situationally, one or the other method may be best applicable. The methods can be applied to the unmixing of common rock-forming minerals present on terrestrial planets, including Earth and Mars, and mixtures of non-geological materials. Raman Match: Application for automated identification of minerals from Raman spectroscopy data Meryem Berrada, Alan McFall, and Bin Chen https://doi.org/10.2138/am-2023-9227 Raman spectroscopy is a powerful, non-destructive analytical tool widely used in various scientific fields, such as chemistry, materials science, and biology. However, this process can be intricate and time consuming, primarily because of the extensive database of Raman spectra. Berrada et al. present the Raman Match application to streamline and automate the sample identification process. This innovative tool simplifies the analysis of Raman spectra through a search-and-match method using the established RRUFF Raman database in the Python programming language. It further offers a user-friendly graphical interface, allowing users to load Raman spectra, identify and fit spectral peaks, match them to reference libraries, visualize the results, and generate publication-ready figures. The implications are significant, particularly for the geoscience and materials science communities, offering a practical solution for scientists and researchers in geoscience and materials science, simplifying and expediting the process of mineral identification with Raman spectroscopy, and ultimately contributing to more efficient and effective scientific investigations and exploration efforts. The transition of the magma plumbing system of Tianchi shield-forming basalts, Changbaishan Volcanic Field, NE China: Constraints from dynamic Fe-Mg diffusion modeling in olivine Ye Tian, Tong Hou, Meng Wang, Ronghao Pan, Xudong Wang, and Felix Marxer https://doi.org/10.2138/am-2023-9296 Tian et al. present a model to perform diffusion modeling with changing and moving boundary conditions during mineral cooling history. This approach is useful in case pyroclastic rocks are lacking and only lava samples are available. It could be successfully applied to other lava samples to improve the accuracy of obtained diffusion timescales. The study combined the Fe-Mg (olivine) diffusion modeling timescales with chemical (bulk-rock geochemistry, mineral chemistry) and textural data (petrography, zoning patterns of olivine) to elucidate the storage and transport conditions of the basaltic magmas of the Tianchi volcano. The results suggest the Tianchi basaltic plumbing system experienced a structural transition from multi-level stalling and subsequent ascent for the TD and BS units to direct ascent from a mid-crust reservoir to the surface for the LFZ unit. Thermoelasticity of phase D and implications for low-velocity anomalies and local discontinuities at the uppermost lower mantle Shangqin Hao, Dapeng Yang, Wenzhong Wang, Fan Zou, and Zhongqing Wu https://doi.org/10.2138/am-2024-9305 Water can be transported into the deep mantle through dense hydrous minerals by subduction, some of which could be detected through geophysical observations because of their distinct physical properties, such as low seismic velocity and high electrical conductivity. Phase D is one of the important hydrous minerals in the uppermost lower mantle (ULM), but its elastic properties under these conditions still need to be clarified. In this study, Hao et al. obtain the elasticity and density of phase D under the conditions of the ULM. The velocities of phase D are comparable to those of major minerals in the ULM, so the enrichment of phase D is not likely to generate seismically detectable low-velocity anomalies, but the strong elastic anisotropy of phase D may explain some seismic anisotropy observations. The results also show that the dehydration of phase D into bridgmanite and stishovite in the ULM produces negligible velocity contrasts but a prominent density increase, which could account for some seismic discontinuities.