American Mineralogist May 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 5; 05-01-2025 Single- and multi-mineral classification using dual-band Raman spectroscopy for planetary surface missions Timothy K. Johnsen and Virginia C. Gulick This paper presents the use of a dual-band co-registered Raman spectrometer for improved mineralogical and scientific yield. The authors developed a classifier with novel multimodal machine-learning methods to discriminate the mineral groups: pyroxene, olivine, potassium feldspar, quartz, mica, gypsum, and plagioclase. The classifier discriminated those minerals between homogeneous samples with 0.997 AUC and detected them in heterogeneous samples with 0.733 AUC (a measurement of accuracy used for multi-classification problems). This research has broad impacts on planetary surface missions. https://doi.org/10.2138/am-2023-9072 Magnesite formation during nesquehonite decomposition in the presence and absence of retained self-generated gases and the role of X-ray amorphous materials as essential stores for CO2 Bree Morgan, Sasha Wilson, Ian C. Madsen, Yesim M. Gozukara, Justin A. Kimpton, and Helen E. Maynard-Casely Magnesite formation mechanisms via crystalline and amorphous phases and the implications for CO2 storage security are poorly resolved. Morgan et al. find that more magnesite forms from nesquehonite when self-generated gases are retained or external CO2 is supplied. The data suggest dehydration-crystallization likely drives magnesite formation; however, solid-gas reactions may also be important in closed-system experiments. The authors propose a novel method to quantify amorphous phases in the system, which are dominant CO2 stores that are often not considered in carbon accounting. https://doi.org/10.2138/am-2023-9202 Episodic magmatism contributes to sub-seafloor copper mineralization: Insights from textures and geochemistry of zoned pyrite in the Ashele VMS deposit Bing Xiao, Huayong Chen, Yuzhou Feng, and Yuanming Pan The question of whether magmatic fluids play an important role in the mineralization processes of ancient VMS deposits affects our understanding of this type of mineralization. The detailed documentation of pyrite textures allowed systematic in situ SIMS sulfur isotope analyses and LA-ICP-MS elemental mapping of zoned pyrite grains to provide significant new insights into the source and evolution of ore-forming fluids in the Early to Middle Devonian Ashele VMS deposit, NW China. The occurrences of alternating Cu-rich and Cu-poor growth zones in pyrite suggest that Cu mineralization of the Ashele VMS deposit is episodic rather than continuous. The study also documented distinct textural patterns and contrasting trace-element compositions and sulfur isotopic signatures in pyrite between the massive sulfide zone and chlorite-quartz-chalcopyrite-pyrite zones. The advantages of pyrite over most other minerals are its ubiquitous occurrences, local high abundances, close spatial-temporal associations with mineralization in VMS deposits, and its complex, pronounced, and robust textural and chemical variations that are readily documented by modern analytical techniques. Textural and geochemical features of zoned pyrite record fluid boiling and magmatic volatile influx in the VMS Cu system, which indicate an incongruous mineralization process. The episodic magmatic-hydrothermal activities could promote mineralization for higher Cu concentration. https://doi.org/10.2138/am-2023-9250 Formation of bonanza Au-Ag-telluride ores in epithermal systems: Constraints from Cu-O isotopes and modeling Shen Gao, Albert H. Hofstra, Kezhang Qin, Xinyu Zou, and Hong Xu This study demonstrates that modeling Cu-O isotope data, can advance understanding of fluid sources and the processes of mineral precipitation in epithermal systems. The results provide new insights into the formation of bonanza Au-Ag-telluride ores in the Te-rich Sandaowanzi deposit, NE China. The results confirm that input of a (300 °C) magmatic fluid containing Au, Ag, Te, and Cu into shallow meteoric water can produce bonanza-grade Au-Ag telluride ores, as proposed previously. The research indicates that the precipitation of Au-Ag telluride takes place at the mixing interface and may occur at greater depths compared to Au-Ag mineralization in adularia-sericite epithermal systems. The Cu-O isotopes and newly developed modeling techniques have potential applications in epithermal and possibly other hydrothermal systems. https://doi.org/10.2138/am-2023-9278 Reexamination of the structure of nanomineral opal-CT using synchrotron X-ray diffraction, transmission electron microscopy, X-ray scattering structure factor, and pair distribution function analyses Seungyeol Lee, Huifang Xu, Hongwu Xu, and Wenqian Xu Previous studies have reported different structures for opal-CT: the interstratification model and the paracrystalline model. The paracrystalline model suggests that the predominant tridymite-like structure is packed in amorphous silica networks, while the interstratification model is related to disordered interlayering and stacking of cristobalite and tridymite domains. This article has identified additional coupled 4-membered and 8-membered rings of [SiO4] tetrahedra formed through twinning and stacking faults. The coupled 4- and 8-membered rings decrease as the crystallinity of opal-CT increases. More broadly, this study demonstrated that the combined approach of synchrotron XRD/PDF (pair distribution function) is a powerful tool for determining the structures of poorly crystallized minerals. The combined method will provide detailed crystallographic information on the phase transformation of natural opal. The new information about the opal-CT structures will help better understand and quantify the transformation from opal-A (diatomaceous clay) to opal-CT during diagenesis (such as the Miocene Monterey Formation in California). https://doi.org/10.2138/am-2024-9333 Development of oxy-symplectites in a slow-spreading lower oceanic crust: Insights from the Atlantis Bank Gabbro Massif, Southwest Indian Ridge Archisman Dhar, Biswajit Ghosh, Tomoaki Morishita, Soumi Chattopadhaya, Debaditya Bandyopadhyay, N.V. Chalapathi Rao, Lydéric France, Du K. Nguyen, Sankhadeep Roy, and Manojit Koley This paper provides a detailed account of the formation of oxy-symplectites in the lower oceanic gabbros recovered from Hole U1473A in Atlantis Bank oceanic core complex, Southwest Indian Ridge. The study sheds light on detecting the oxidation agent and how the entire process controls the textural and mineralogical modifications of lower oceanic crust during subsolidus cooling. https://doi.org/10.2138/am-2024-9350 Heterogeneous distribution of Al-hematite regulated by hydrologic regime in a basaltic laterite of Hainan Island, South China: Implications for the aqueous history of Mars Xiaorong Qin, Wei Tan, Hongping He, Jiacheng Liu, Qi Tao, Jianxi Zhu, Hongyan Wei, Lianying Luo, Keyan Chen, Tianqi Zhang, and Shichao Ji This study investigates the effects of aqueous environments on the formation and preservation of Al-hematite in a basaltic weathering profile from a 48 m long drill hole from Hainan Island in South China. The results demonstrate a genetic link between the Al content of hematite and environment of formation and highlight the influence of hydrodynamic conditions on the formation and preservation of Al-hematite. Comparative study suggests that the high abundance of Al-hematite found in certain martian outcrops may suggest the presence of transient liquid water with a slightly higher flow rate, e.g., episodic floods and intense precipitation, which would imply short-term warmer and wetter conditions on Mars. https://doi.org/10.2138/am-2024-9374 Atomic-scale visualization and quantification of lithium in lepidolite by AC-TEM-EELS: Implications for pegmatite genesis and advancing lithium extraction techniques Mao-Wen Yuan, Xiao-Wei Li, Joshua J. Schwartz, Zhi-Dan Zhao, Zhao-Ge Hao, Jia-Wei Liu, Masroor Alam, Guo-Chen Dong, Wan-Ming Yuan, and Zi-Hao Wen This study presents an analytical solution to determining lithium contents in lepidolite, which has potential to unlock otherwise overlooked lithium sources. Specifically, the authors use a novel approach that combines spherical aberration-corrected transmission electron microscopy (AC-TEM) in conjunction with electron energy loss spectroscopy (EELS) to visualize and quantify lithium in lepidolite. This approach analyzes the spatial distribution and concentration of lithium in mica, thereby characterizing the economic potential of the mineral. The analytical approach provides a significant advantage over traditional methods, such as electron microprobe and LA-ICP-MS analyses, which rely on empirical formula calculations and are susceptible to inaccuracies due to fluid or minor mineral inclusions. The findings have the potential to significantly advance the understanding of cation ordering in lepidolite, its polytypes, chemical compositions, and economic potential, as well as refining lithium extraction techniques. https://doi.org/10.2138/am-2024-9436 The use of X-ray micro-computed tomography to visualize and quantify lithium-bearing silicate minerals in pegmatites: Examples from the Tanco Pegmatite, Manitoba, Canada Catriona M. Breasley, Ivan R. Barker, Robert L. Linnen, Tânia Martins, and Lee A. Groat This paper investigates X-ray micro-computed tomography (micro-CT) as a technique for visualization and quantification of spodumene in pegmatite samples in a three-dimensional and non-destructive way. This technique can capture 3D spatial information and quantify the minerals present in samples. Spodumene is a critical mineral and the main source of hard-rock lithium. Understanding the textures and proportions of spodumene helps with understanding deposit formation and in developing efficient mining and metallurgical processing strategies. https://doi.org/10.2138/am-2024-9439 Titanium substitutions in garnet at magmatic, granulite facies, and high-pressure granulite facies conditions Jay J. Ague, Duncan S. Keller, Michael R. Ackerson, and Megan Holycross An analysis of existing experimental results shows that Ti entry into garnet is complex and governed by multiple substitutions. A comparison of experimental and natural garnet compositions indicates that garnets likely lose substantial Ti (and alkalis) during cooling by processes such as diffusion or interface-coupled dissolution-reprecipitation. This Ti can be sequestered locally in precipitates of rutile and/or ilmenite within the host garnet or lost to the rock matrix. https://doi.org/10.2138/am-2024-9442 Mechanistic understanding of the dehydroxylation reaction of smectites: Insights from reactive force field (ReaxFF) molecular dynamics simulation Pengyuan Gao, Yingchun Zhang, Xiandong Liu, and Xiancai Lu Reactive molecular dynamics simulations reveal thermal reaction mechanisms and high-temperature transformations of smectites. The findings provide a theoretical basis for distinguishing cv (cis-vacant) and tv (trans-vacant) smectites using thermogravimetric analysis. The data collected indicate that montmorillonites have cv structure, and almost all smectites from China are cv. https://doi.org/10.2138/am-2024-9445 Allanite-(Sm), CaSm(Al2Fe2+)(Si2O7)(SiO4)O(OH), the third samarium mineral from Jordanów Śląski, Lower Silesia, Poland Adam Pieczka, Bożena Gołębiowska, Adam Włodek, Marcin Stachowicz, Petras Jokubauskas, Jakub Kotowski, Krzysztof Nejbert, Adam Szuszkiewicz, and Krzysztof Woźniak The authors document allanite-(Sm), ideally CaSm(Al2Sc)(Si2O7)(SiO4)O(OH), the third recognized mineral of samarium. It was discovered in a granitic pegmatite in contact with rodingite-like calc-silicate rocks in a serpentinite quarry at the locality in Poland. Pieczka et al. show crystallochemical and structural data for this new mineral as well as approximate formation conditions that could favor the crystallization of this epidote-supergroup mineral. https://doi.org/10.2138/am-2024-9453 The “breathing” Earth at Solfatara-Pisciarelli, Campi Flegrei, southern Italy (2005–2024): Nature’s attenuation of the effects of bradyseism Annamaria Lima, Robert Bodnar, Benedetto De Vivo, Frank Spera, Harvey Belkin This Letter addresses an issue of societal relevance. Campi Flegrei (CF) is a vast volcanic area west of Naples, home to approximately 1.5 million people. It represents one of the highest risk areas in Italy for continuing slow ground deformation (bradyseism) currently ongoing. Understanding the causes of unrest allows the authors to propose geoengineering approaches to reduce the impact of bradyseism, in particular the volcanic and seismic activity that arises from fluid pressure build-up at CF. https://doi.org/10.2138/am-2024-9516 Estimating the iron oxidation state of serpentinite using X-ray absorption fine structure spectroscopy Kazuki Yoshida, Atsushi Okamoto, Ryosuke Oyanagi, Yasuhiro Niwa, and Masao Kimura Iron in serpentinite, found in various oxidation states, plays a vital role in geologic processes. X-ray absorption near-edge structural spectroscopy is a powerful tool for characterizing its redox state. However, a general scheme for estimating the oxidation state of Fe in multiple Fe-bearing minerals in serpentinite has not been established. The method used in this study effectively estimates iron oxidation state, even in complex mixtures, and provides insight into the redox state evolution of serpentinization. https://doi.org/10.2138/am-2024-9571