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 8; 08-01-2025 Morphological approach to understanding mineral alteration and nanoparticle formation under alkaline conditions using granitic rock thin sections Eungyeong Kim, Sung Pill Hyun, Ho Young Jo The cement components in deep geological disposal facilities (DGFs) for spent nuclear fuel can increase groundwater pH, potentially altering minerals within natural barriers. Previous studies investigating mineral alterations in deep geological rocks have used single mineral powder samples with high surface areas, which do not accurately represent the characteristics of real field-based geological environments involving coexisting minerals. In this study, Kim et al. investigated the alterations of various minerals (biotite, quartz, albite, chlorite, and K-feldspar) using samples that represent the exposed rock surface on the fracture planes of deep crystalline rocks. The morphological characteristics of granite rock thin sections exposed to alkaline aqueous solutions were examined using optical microscopy, atomic force microscopy, micro-X-ray fluorescence, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Furthermore, they investigated how mineral alterations affect the formation of secondary-phase nanoprecipitates. This study integrates multifaceted processes (such as dissolution, precipitation, and colloid formation) to provide a comprehensive understanding of the complex interplay between dissolution and precipitation reactions and demonstrates the importance of this integration using morphological analysis to visually exhibit these complex phenomena. https://doi.org/10.2138/am-2024-9261 Viscosity measurements of selected lunar regolith simulants Simon Stapperfend, Donald Dingwell, Kai Hess, Jennifer Sutherland, Axel Müller, Dirk Müller, Michael Eitel, Julian Baasch, Stefan Linke, Enrico Stoll Stapperfend et al. measured the viscosities of a selected set of lunar regolith simulants at glass transition and superliquidus temperatures using differential scanning calorimetry and concentric cylinder viscometry. Results show that basaltic simulants have lower viscosities, which favors their use in lunar 3D printing due to their lower melting temperatures. The study also compares these findings with six viscosity models, crucial for advancing lunar construction techniques. An evaluation has been conducted to assess the suitability of various lunar regolith simulants for use in additive manufacturing techniques utilizing molten lunar regolith. https://doi.org/10.2138/am-2023-9263 Nanoscale characterization of chrysocolla, black chrysocolla and pseudomalachite from supergene copper deposits of Atacama Desert of northern Chile Zia Steven Kahou, Anne-Magali Seydoux-Guillaume, Pierre-Marie Zanetta, Stéphanie Duchêne, Stéphanie Brichau, Eduardo Campos Kahou et al. conducted the first transmission electron microscopy (TEM) study on chrysocolla, black chrysocolla, and pseudomalachite samples from Mina Sur and Damiana supergene copper deposit. Chrysocolla and black chrysocolla are not homogeneous crystals but assemblages of nanoparticles embedded in an amorphous matrix. Scanning TEM (STEM) images reveal that chrysocolla presents rounded Cu-rich nanoparticles embedded in an amorphous matrix, while black chrysocolla presents needle-shaped Mn-rich and some rounded Cu-rich nanoparticles embedded in an amorphous matrix. Pseudomalachite is a massive polycrystalline mineral highlighted by large nanocrystal grains of ~500 nm. The results highlight the powerful advantage of TEM studies to yield important details about crystal structure and organization at nanoscales, which contributes to better understanding of textural characteristics and supergene copper minerals formation. https://doi.org/10.2138/am-2024-9300 Identification of Hydroandradite in CM Carbonaceous Chondrites: A Product of Calc-Silicate Alteration on C-Complex Asteroids Laura Jenkins, Martin Lee, Luke Daly, Ashley King, Peter Chung, Sammy Griffin, Shijie Li Hydroandradite, a water-bearing garnet, was found in two meteorites, Shidian and Kolang. This is the first identification of hydroandradite occurring in meteorites. Its occurrence near other hydrous minerals as well as in heated lithologies has implications for both its formation temperature and the temperatures at which it is stable. Hydroandradite may be found in more meteorites in the future. https://doi.org/10.2138/am-2024-9389 Identification of the nature of recycled carbonates in the mantle: Insights from Mo-Mg isotopic pair Ming Lei, Zhengfu Guo, Donald Dingwell, Jie Li, Jianlin Chen Lei et al. demonstrated that recycled carbonate sediments at sub-arc depths in the mantle may increase their δ98/95Mo values without significantly affecting their δ26Mg values, whereas recycled carbonate sediments at post-arc depths in the mantle would decrease both δ98/95Mo and δ26Mg values. Therefore, the Mo-Mg isotopic pair may be a unique tool for determining whether the mantle contains recycled carbonates and for identifying the types of carbonates involved during oceanic subduction. https://doi.org/10.2138/am-2024-9408 Growth and crystallographic features of interpenetrant twins in natural diamonds Kaiyue Sun, Taijin Lu, Mingyue He, Zhonghua Song, Jian Zhang, Jie Ke Sun et al. investigated the crystallographic features and growth mechanism of a group of interpenetrant twins in natural diamond from the Republic of Congo. Three types of theoretical twin models of natural diamond with interpenetrant twins have been established. From the observation of crystal morphology, all the samples exhibit a cubic habit with deformation. These crystals have a rough appearance and fibrous growth layers, indicating rapid crystallization under high driving force conditions. Combined with the growth features observed by the CL technique, two patterns emerge regarding the formation of interpenetrant twins in natural diamonds: 1) Grain originates in the nucleation stage of crystals in the form of twinned positions; and 2) The orientation of the growth layer arrangement changes during crystal growth. Moreover, a mixed type of twin structure was observed, indicating the complexity of the diamond twin growth process, which involves a transformation in the crystallization habit of the crystal. https://doi.org/10.2138/am-2024-9426 Determination of the oxidation state of iron in calcic pyroxene using the electron microprobe flank method Yonghua Cao, Chang-Ming Xing, Christina Wang, Xianquan Ping Pyroxene is an important host mineral for ferric iron in igneous and mantle rocks. The oxidation state of iron (e.g., Fe3+/ΣFe) in pyroxene serves as a direct proxy for estimating the oxygen fugacity of magma and the mantle. Many techniques have been developed to determine the Fe3+/ΣFe ratio of pyroxene. The electron probe microanalysis (EPMA) flank method has several advantages, including easy accessibility, a micrometer-scale analysis area, and high efficiency. However, the application of this method to pyroxene groups has been explored in only a few studies and is further limited by a lack of appropriate calibration standards. In this study, Cao et al. examined nine natural pyroxene samples, including one aegirine, one hedenbergite, one diopside, and six augites. Based on the evaluation of these pyroxene samples, a multiple linear regression approach using the flank-method data, Fe2+, and ΣFe contents yields Fe2+ content and Fe3+/ΣFe ratios with an error of ±0.3 wt% and ±0.06, respectively, for calcic pyroxene containing 7 wt% total FeO. These well-characterized natural pyroxene samples can serve as reference materials for determining the Fe3+/ΣFe ratio in unknown calcic pyroxene. https://doi.org/10.2138/am-2024-9467 Formation mechanism of boehmite and diaspore in karstic bauxites: Trace element geochemistry in source materials using a large sample geochemical dataset and a random forest model Hui Qi, Sheng-Qiang Zhang, Kai-Ning Lv, Guo-Li Yuan, Pei-Pei Dong, Ying-Jie Li, Jun Li, Xuefei Liu Boehmite and diaspore are two economic ore minerals of karstic bauxites. A random forest (RF) model of machine learning was employed to extract the combined characteristics of trace elements in boehmite-type bauxite (BTB) and diaspore-type bauxite (DTB). The BTB predominantly exhibits higher median concentrations of Co, Ni, V, and Cr, while the DTB shows a more significant enrichment in U, Hf, Th, and Zr. BTB exhibits consistent characteristics with lateritic bauxite weathered from basic rock and its parent rocks. Similarly, DTB displays consistent characteristics with lateritic bauxite weathered from intermediate-felsic rock and their parent rocks. Through studying the relationship between Ni content and Fe3+/Fe2+ ratios, it has been discovered that the presence of trace elements like Ni in source materials can affect or regulate the ore-forming process, ultimately driving the transformation of gibbsite into either boehmite or diaspore. https://doi.org/10.2138/am-2024-9499 High-temperature Raman spectroscopy of K2Ca(CO3)2 bütschliite and Na2Ca2(CO3)3 shortite Garrett Zeff, Quentin Williams This study sheds light on the stability and vibrational properties of alkali/calcium carbonate minerals at high temperatures. The variation in anharmonicity between different vibrational modes of each of the low-temperature phases is assessed, yielding insights into inter-carbonate group couplings. https://doi.org/10.2138/am-2024-9500 Effects of high-temperature annealing and low-temperature metamictization on Archean zircon: Constraints from U-Pb isotopes, trace elements, and Raman dating Carlos Ribeiro, Elton Dantas, Reinhardt Fuck Zircon is a common accessory mineral used to track high-temperature events, although its application to low-temperature chronometry is still debated. This study combines U-Pb in zircon dating, trace elements, and Raman spectroscopy to constrain the different behavior and thermal evolution of distinct lithologies at the same outcrop. The results indicate that high-temperature partial melting is unable to recover the structure of zircon grains, resulting in strong radiation damage and the influx of non-formula elements at lower temperatures. On the other hand, assimilation in mafic magmas leads to structure recovery, preservation of internal textures, and homogenization of trace elements. Raman zircon dating yields similar ages to U-Pb lower intercept ages, highlighting the potential of metamict zircon to track low-temperature events. https://doi.org/10.2138/am-2024-9502 Discriminating ionic mobility between diffusivity and electrical conductivity experiments on Earth's silicate materials Xiaozhi Yang Ionic diffusivity and electrical conductivity are the two most typical transport properties of Earth's silicate materials, and a genetic link between them has long been assumed. Yang demonstrated for the first time that the two transport properties of silicate materials cannot be correlated with each other; the theoretical and experimental reasons are discussed. https://doi.org/10.2138/am-2024-9523 Formation of nano-CdS solid solution: A mechanism for Cd enrichment in sphalerite Lei Yan, Yu Fan, Jun Huang, Tong Zuo, Fangyue Wang, Taofa Zhou Yan et al. investigates the mechanism for Cd enrichment in sphalerite. In relatively Cd-poor areas, Cd was found to occur as a lattice substitution for Zn, whereas in Cd-rich areas, a new nano-scale occurrence state of Cd, namely nano-CdS solid solution, was discovered. Reactivation and dynamic recrystallization induced by plastic deformation of sphalerite, as well as solid solution precipitation caused by cooling, are important mechanisms for Cd enrichment. The coherent interface relationship between CdS and ZnS is crucial for the formation and stable existence of nano-CdS solid solution. This study provides new nanoscale mineralogical evidence and insights for understanding the complex distribution characteristics of dispersed elements in sphalerite. https://doi.org/10.2138/am-2024-9524 High pressure single crystal X-ray diffraction and Raman spectroscopy of boltwoodite, K0.63Na0.37[(UO2)(SiO3OH)](H2O)1.5 Carmen Chamberlain, Jennifer Szymanowski, Peter Burns Chamberlain et al. report the first crystallographic and spectroscopic study of a uranyl mineral at high pressures. The uranyl silicate boltwoodite was selected for study because uranyl silicates are common in oxidized portions of uranium ore deposits, it forms when spent nuclear fuel is altered, good-quality natural crystals are available, and it has a relatively simple structure. A collection of single-crystal X-ray diffraction data and Raman spectra for multiple crystals contained in a diamond-anvil cell yielded insight into structural changes over the pressure range from ambient to 16.8 GPa. No obvious phase transitions were observed, with most changes to accommodate increasing pressure achieved through adjustments in the interlayer and increased corrugation of the uranyl silicate sheets. https://doi.org/10.2138/am-2024-9531 Hematite (U-Th)/He thermochronometry unveils unique exhumation history: An example from the Dexing porphyry copper deposit, Southern China Hong Zhang, Yu Wang, Fang An, Honglin Yuan, Jianfeng Gao Hematite (U-Th)/He thermochronology can be used to indicate the uplift and cooling history near the crust surface based on the optimized conditions that prevent U-loss and enhance accuracy. This study marks the first instance of integrating hematite, zircon, and apatite (U-Th)/He data to comprehensively track the temperature fluctuations associated with the uplift and exhumation history of porphyry deposits in China. Based on detailed hematite (U-Th)/He thermochronology analysis, the Dexing giant porphyry copper Deposit may have experienced a relatively long thermal history, with exhumation and uplift occurring at 112 Ma, and rapid uplift spanning a time range of 11.2 to 8 Ma. https://doi.org/10.2138/am-2024-9555 Nanoscale Insights into Weathering of Ti-Bearing Minerals and Heterogeneous Crystal Growth Mechanisms of Ti nano minerals in Altered Volcanic Ash Chen Liu, Qian Fang, Hanlie Hong, Lulu Zhao, Yanling Yang, Shuling Chen Using a series of advanced nanoscale techniques, including focus ion beam, high-resolution transmission electron microscope (FIB-HRTEM), electron energy loss spectroscopy (EELS), and nano-computed tomography (Nano-CT), Liu et al. demonstrated that the growth of anatase and brookite nanoparticles within the volcanic ash matrix is regulated by Ostwald ripening (OR) with minor semi-oriented attachment (OA) and recrystallization. Meanwhile, the growth of brookite crystals in altered srilankite particles, which exhibits crystallization by particle attachment (CPA), is predominantly controlled by the oriented attachment mechanism. Under chemical weathering, the edges of TiO2 crystals tend toward amorphization, Ti4+ gradually reducing to the Ti3+ valence state. Following the alteration of srilankite, primary brookite crystals form in situ, initially growing into incomplete oriented particles through oriented attachment. Subsequently, these oriented particle fragments further grow by attaching to primary crystals in the matrix, forming large brookite crystals with consistent crystallographic orientations. This comprehensive dataset advances our understanding of the formation of authigenic/secondary Ti-bearing particles during diagenesis and the detailed alteration processes of TiO2 during the chemical weathering process in sedimentary systems. https://doi.org/10.2138/am-2024-9573