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 far-right tab. 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, then authenticate from the American Mineralogist menu (here directly). Once at the portal page, click the right-side 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 open to anyone who registers on the site. Thank you for reading American Mineralogist. Sincerely, Hongwu Xu Don Baker American Mineralogist Volume 109; Number 10; 10-01-2024 High-pressure phase transition in clinochlore: IIa polytype stabilization Benedetta Chrappan Soldavini, Davide Comboni, Michael Hanfland, and Marco Merlini https://doi.org/10.2138/am-2023-9277 Soldavini et al. conducted in-situ single crystal X-ray diffraction on natural clinochlore under pressures up to 20 GPa at room temperature and 600 K. A phase transition at 9 GPa was observed, revealing a shift from the IIb-4 triclinic to the IIa-1 monoclinic polytype. This transition showed reversibility and led to a significant reduction in disorder. The bulk modulus decreased from 81.2(13) to 56.0(6) GPa, indicating stabilization of a more compressible structure. The same transition occurred at 7.8 GPa during high-temperature experiments at 600 K, suggesting a negative P/T slope. Therefore, stabilizing the IIa polytype could prevent chlorite's destabilization and dehydration during high P-T processes, such as impact events. In these contexts, the occurrence of metastable transformation has potential implications for volatile retention during planetary accretion. Trace element fractionation in magnetite as a function of Fe depletion from ore fluids at the Baijian Fe-(Co) skarn deposit, eastern China: Implications for Co mineralization in Fe skarns Guang Wen, Jian-Wei Li, Albert H. Hofstra, Daniel E. Harlov, Xin-Fu Zhao, Heather A. Lowers, and Alan E. Koenig https://doi.org/10.2138/am-2023-9105 In-situ geochemical analyses of magnetite from the Baijian Fe-(Co) skarn deposit in eastern China, coupled with quantitative (Rayleigh and equilibrium) modeling, show that progressive precipitation of magnetite controls the trace element composition of both the fluid and magnetite during Fe skarn mineralization. This process significantly decreases the concentrations of compatible elements (Ni and V) and increases the concentrations of incompatible elements (Zn, Mn, and Co) in magnetite. The observed variations in the ratios of incompatible/compatible elements (e.g., Co/Ni, Zn/V, and Zn/Ni) in magnetite can be explained by Rayleigh fractionation. As magnetite continues to precipitate, the Co/Fe ratio in the fluid increases, causing Co to precipitate in late-stage sulfides. The findings further suggest that Fe skarn deposits with substantial Fe reserves (e.g., >50 Mt Fe) can potentially contain significant amounts of Co, thus offering new resources to meet the growing demand for this metal. This article is part of the “Critical Minerals for a Sustainable Future” special collection. Evidence for oceans pre-4300 Ma confirmed by preserved igneous compositions in Hadean zircon Emilia M. Cameron, Tyler B. Blum, Aaron J. Cavosie, Kouki Kitajima, Lutz Nasdala, Ian J. Orland, Chloe E. Bonamici, and John W. Valley https://doi.org/10.2138/am-2023-9180 Cameron et al. demonstrate that primary, well-preserved domains can be recognized using standard methodologies even in zircons older than 4000 Ma. The results refute the hypothesis that mildly elevated δ18O values in Hadean zircons result from alteration. The results show that pristine domains in Jack Hills zircons that preserve primary unaltered δ18O values representative of their growth in Hadean magmas can be identified if carefully selected based on objective criteria. This study supports the conclusion that the surface of early Earth cooled and had liquid-water oceans before 4300 Ma. Thus, conditions were habitable for life 800 myr before the oldest documented microfossils. This article is part of the “Isotopes, Minerals, and Petrology: Honoring John Valley” special collection. Experimental vs. natural fulgurite: A comparison and implications for the formation process A. Zeynep Çalışkanoğlu, Corrado Cimarelli, Donald B. Dingwell, and Alessandra S.B. Camara https://doi.org/10.2138/am-2023-9192 Fulgurites, glassy formations from lightning strikes, offer insights into past environments and prebiotic chemistry. Çalışkanoğlu et al. compared a natural fulgurite in Eastern Turkey to one created in a lab, finding similar structures and, using Raman spectroscopy, estimated a formation temperature gradient. The authors also measured cloud-to-ground lightning discharge parameters, suggesting a current range for the natural fulgurite's formation. This research enhances the understanding of fulgurite formation and its implications for Earth's history. Illitization of smectite influenced by chemical weathering and its potential control of anatase formation in altered volcanic ashes Chen Liu, Qian Fang, Hanlie Hong, Qian Song, Kaipeng Ji, Nina Gong, Xibing Shen, and Thomas J. Algeo https://doi.org/10.2138/am-2023-9125 Through investigation of the fine structure of clay minerals and in-situ nano-mineralogy of Ti-bearing minerals from K-bentonite and meta-analysis of geochemical compositional data compilation of 384 K-bentonite layers with a global distribution, Liu et al. discovered that chemical weathering could promote the illitization reaction, which may jointly influence the formation of Ti oxides. Interstratified illite-smectite can adsorb Ti during the weathering and provide a suitable site for the nucleation of anatase and enrichment of titanium. This study unravels the role of chemical weathering in the illitization of smectite and its effect on the formation of Ti oxides. The comprehensive dataset advances our understanding on the formation of interstratified illite-smectite, illitization process, and related geochemical cycling in sedimentary systems. The coupling revealed in this study represents a linkage between sedimentary-basin evolution, environmental change, clay-mineral transformation, and nano-mineral neoformation. A modified genetic model for multiple pulsed mineralized processes at the giant Qulong porphyry Cu-Mo mineralization system Youye Zheng, Xin Chen, Sangjiancuo Luo, Qiong Ci, Le Zhang, Jiangang Wei, Shunbao Gao, and Hao Lin https://doi.org/10.2138/am-2023-9145 To gain deeper insights into the processes that led to the formation of porphyry copper deposits (PCD), Zheng et al. obtained data from cathodoluminescence (CL) imaging, in-situ trace elements, and Sr isotopes of newly discovered scheelite (Sch 1, Sch 2, and Sch 3) found in three generations of vein types within the giant Qulong porphyry Cu-Mo mineralization system. These scheelite veins record at least three superimposed, episodic hydrothermal pulses. Volatiles originating from mafic rocks, injected into the porphyry metallogenic system, assume a pivotal role in shaping PCD formation. These findings shed light on the potential for identifying complementary metal endowments of W-Cu-Mo and extending the metallogenic scope of PCDs within collision zones. Lead and noble gas isotopic constraints on the origin of Te-bearing adularia-sericite epithermal Au-Ag deposits in a calc-alkaline magmatic arc, NE China Shen Gao, Albert H. Hofstra, Kezhang Qin, Xinyu Zou, Michael J. Pribil, Andrew G. Hunt, Andrew H. Manning, Heather A. Lowers, and Hong Xu https://doi.org/10.2138/am-2022-8552 Gao et al. present the in-situ study of Pb isotopes in tellurides (including altaite, petzite, and hessite) in epithermal systems conducted using a femtosecond laser ablation MC-ICP-MS. The authors combined in-situ Pb isotope analysis with He, Ne, and Ar isotope and microthermometric analysis of fluid inclusions in ore and gangue minerals from two Te-rich and two Te-poor epithermal Au-Ag deposits in an Early Cretaceous magmatic arc in northeastern China. The results were used to determine the proportions of mantle and crustal material as well as fluid evolution in Te-rich and Te-poor Au-Ag deposits. The isotopic results obtained on low Pb-content minerals are useful for tracing the source of metals in hydrothermal deposits. Wenlanzhangite–(Y) from the Yushui deposit, South China: A potential proxy for tracing the redox state of ore formation Peng Liu, Guowu Li, Ningyue Sun, Wei Yao, Hong Yu, Yongfei Tian, Wenqiang Yang, Fengshang Zhao, and Nigel J. Cook https://doi.org/10.2138/am-2023-9220 Liu et al. report a new V-HREE-bearing silicate mineral species, wenlanzhangite-(Y), which is a vanadiferous derivate of jingwenite-(Y) [Y2Al2V4+2(SiO4)2O4(OH)4] coexisting with jingwenite-(Y) in bedded/massive ores at Yushui, South China. The occurrence of wenlanzhangite-(Y) indicates a relatively more reducing hydrothermal environment, causing a reduction of V5+ in oxidized fluids to V3+ and thus represents a useful proxy for tracing the redox state of ore formation. High-resolution SIMS U-Th-Pb geochronology of small-size (<5 μm) monazite: Constraints on the timing of Qiuling sediment-hosted gold deposit, South Qinling Orogen, central China Lei Chen, Albert H. Hofstra, Xian-Hua Li, Qiu-Li Li, Yu Liu, Xiao-Xiao Ling, Xiao-Yan Liu, and Wei Jian https://doi.org/10.2138/am-2023-9210 This study presents an example of monazite compositional alteration and hydrothermal monazite growth of U-Th-Pb ages caused by coupled dissolution-reprecipitation reactions. It is crucial to examine the monazite textures and recognize alteration textures before carrying out isotopic dating of monazite collected from hydrothermal ore deposits. This study also demonstrates that monazite could record early hydrothermal events and not be affected by later hydrothermal alteration. Combined with textual and compositional characterization, the high-resolution SIMS U-Th-Pb dating technique on small-size monazite represents a powerful tool for determining the timing of mineralization, especially in the ore deposit without suitable geochronometers to record the hydrothermal process. This work is of interest to researchers studying metallic mineralization, major and trace elements of hydrothermal accessory minerals, and the geochronology of hydrothermal deposits. An evolutionary system of mineralogy, Part VIII: The evolution of metamorphic minerals Shaunna M. Morrison, Anirudh Prabhu, and Robert M. Hazen https://doi.org/10.2138/am-2023-9004 The eighth installment of the "Evolutionary System of Mineralogy" explores relationships among 1220 species of metamorphic minerals. Metamorphic rocks display characteristics of an evolving chemical system, with significant increases in mineral diversity and chemical complexity over the first four billion years of Earth history. Earth's first metamorphic rocks were thermally altered xenoliths and contact zones (hornfels and sanidinite facies) associated with early Hadean igneous activity (>4.5 Ga). The appearance of new Hadean lithologies, including clay-rich sediments, arkosic sandstones, and carbonates, provided additional protoliths for thermal metamorphism prior to 4.0 Ga. Mountain building and erosion exposed extensive regional metamorphic terrains, with lithologies corresponding to a sequence of metamorphic facies. More recently, rapid subduction and rebound of crustal wedges, coupled with a shallowing geothermal gradient, has produced distinctive blueschist, eclogite, and ultrahigh-pressure metamorphic suites (<1.0 Ga). The evolution of metamorphic minerals thus exemplifies changes in physical and chemical processes in the crust and upper mantle that characterize Earth's first 4 billion years. Gamma-enhancement of reflected light images as a routine method for assessment of compositional heterogeneity in common low-reflectance Fe-bearing minerals Qiaoqiao Zhu, Guiqing Xie, Nigel J. Cook, Cristiana L. Ciobanu, and Hui Wang https://doi.org/10.2138/am-2023-9114 Reflectance variations of Fe-bearing ore minerals (magnetite, wolframite, and tetrahedrite-tennantite) and transparent minerals (garnet) were revealed using the gamma correction method, which enhances optical digital signal differences obtained under reflected light using an optical microscope. Gamma-enhanced reflectance variation is either the same as the gray value change seen on backscatter electron (BSE) images or contrasting, yielding a convincing linkage between reflectance variation and compositional heterogeneity. This method can even assess the compositional heterogeneity of wolframite, which is nearly impossible to observe on BSE images. Fe-rich domains in these minerals are expected to have higher reflectance than Fe-poor domains. Gamma correction can be used as a routine method to assess compositional heterogeneity and textural variation for certain Fe-bearing minerals before quantitative analysis. Gamma correction is an alternative, optical-based technique that can be used instead of or complement BSE imaging. Polysomatic intergrowths between amphiboles and non-classical pyriboles in magnetite: Smallest-scale features recording a protracted geological history Yuri Tatiana Campo Rodriguez, Cristiana L. Ciobanu, Ashley Slattery, Nigel J. Cook, Maria Emilia Schutesky, Kathy Ehrig, Samuel A. King, and Jie Yao https://doi.org/10.2138/am-2023-9188 Campo Rodriguez et al. report a nanoscale study of non-classical pyriboles (NCPs) within magnetite cores from the Jatobá Ni-bearing IOCG deposit, Carajás district, Brazil. The occurrence contains one of the widest ranges of chain silicates ever recorded, from simple intergrowths of single to triple Ibeam zippers, including pyroxene slabs, to longer NCP polysomes up to 15-Ibeam chains. Clinojimthompsonite (Cjim) is observed for the first time within magnetite. Co-crystallization of double- and triple-chain silicate structures with rhythmic intergrowths as larger blocks along b is often accompanied by rhythmic Ca-Fe zonation along a, supporting primary NCP crystallization via self-patterning during amphibole growth within magnetite in a close-to-equilibrium system. The multi-stage amphibole-NCPs generations in magnetite emphasize the interpretive value of magnetite for overprinting events in terranes with protracted geological histories. The discovery of Ce-rich hornblende provides new avenues to understand the early, alkali-calcic alteration stages of IOCG systems and models for REE incorporation into and subsequent release from chain silicates. Mineralogical and geochemical facets of the massive deposition of stibnite-metastibnite at a seafloor hydrothermal field (Wakamiko Crater, Kagoshima Bay, Ryukyu Volcanic Arc) Vesselin Dekov, Yukako Furuma, Bleuenn Guéguen, Lukas Klose, Kazutaka Yasukawa, Motoaki Morita, Dan Asael, Toshiro Yamanaka, Luca Bindi, Andrea Koschinsky, Bernhard Pracejus, and Yasuhiro Kato https://doi.org/10.2138/am-2023-9096 Stibnite and metastibnite (described for the first time at the seafloor) precipitate as massive boulders in a submarine crater of the Ryukyu volcanic arc. The study shows that hydrothermal conditions of low temperatures (<50 °C) and low values of pH (<6) are favorable for the precipitation of stibnite on the seafloor. Metastibnite deposition appears to result from rapid quenching of hot hydrothermal fluid when mixed with cold seawater and rapid precipitation at the interface between stibnite and vent fluid. By investigating the mineralogy and geochemistry (including S isotope composition) of the hydrothermal deposits along with the geochemistry of the venting fluids, this work provides insight into the precipitation conditions of stibnite at seafloor hydrothermal sites. Memorial of Larry Wayne Finger (1940–2024) https://doi.org/10.2138/am-2024-M102024