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 here (http://www.minsocam.org/MSA/Ammin/AM_NotableArticles.html). 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 MSA membership, then authenticate in from the American Mineralogist menu (here<http://www.msapubs.org/> directly). Once at the portal page, click the right-side American Mineralogist link, enter your user name (e-mail address), and your password (membership number). Then search via your browser’s search tools for the paper you want to read. (On Rachel’s computer, it is control-f but we think that is little different for everyone.) Note that on GSW you can sign up for a table of contents to be sent 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 Don Baker Crystal chemistry and thermodynamic properties of zircon structure-type materials https://doi.org/10.2138/am-2022-8632 Strzelecki et al. evaluated recent advances in the crystal chemistry and thermodynamic properties of zircon structure-type materials, identifying several knowledge gaps. The review will help researchers develop a fundamental understanding of zircon-type minerals and promote using zircon-type materials for such applications as actinide waste forms and environmental barrier coatings in aeronautical engineering. Thermal and combined high-temperature and high-pressure behavior of a natural intermediate scapolite https://doi.org/10.2138/am-2023-8962 Scapolites, which are intermediate between the marialite and meionite end members, usually show a primitive symmetry. Lotti et al. reported an intermediate scapolite with an unusual I4/m symmetry, and they investigated it at high-T and combined high-T and high-P with in situ diffraction techniques. Elastic behavior and structural deformation mechanisms have been described, and a phase transition observed. Implications on the potential metastable preservation of I4/m scapolites are also discussed. Crystal structure, hydrogen bonding, and high-pressure behavior of the hydroxide perovskite MgSi(OH)6: A phase relevant to deep subduction of hydrated oceanic crust. https://doi.org/10.2138/am-2022-8889 Welch et al. reported for the first time the full crystal structure, including hydrogen bonding, of the high-pressure synthetic hydroxide perovskite MgSi(OH)6. This phase is considered to likely play a significant role in the hosting and transfer of H2O in the Earth's deep mantle at cold subduction zones. Experiments to 8 GPa described here provide insights into the structural behavior of MgSi(OH)6 and provide an essential basis for future experimental and computational studies of its stability. Equilibrium Sn isotope fractionation between aqueous Sn and Sn-bearing minerals: Constrained by first-principles calculations https://doi.org/10.2138/am-2022-8804 Sun et al. performed first-principles calculations on the equilibrium Sn isotopic fractionation between aqueous Sn species and minerals. Major outcomes are: (1) The Sn isotope geothermometers of cassiterite-stannite and malayaite-stannite have been established; (2) The controlling factors of Sn isotope fractionation between different aqueous Sn complexes are revealed; (3) The precipitation of aqueous Sn complexes into various tin minerals (malayaite, cassiterite and stannite) lead to the fractionation of Sn isotope in different degrees and directions. The calculated results are essential for further application of Sn isotope in various Sn-involved geological processes. Raman Spectroscopic Investigation of Selected Natural Uranyl Sulfate Minerals https://doi.org/10.2138/am-2023-8932 Spano et al. reported Raman spectra of 18 uranyl sulfate minerals. To better understand underlying structural and chemical features that give rise to spectroscopic observables, they related differences in structural topology, charge balancing cations, and locality of origin to features observed in the Raman spectra of selected natural uranyl sulfates. Modified magnetite and hydrothermal apatite in banded iron-formations and its implications for high-grade Fe mineralization during retrogressive metamorphism https://doi.org/10.2138/am-2022-8525 Magnetite (an abundant and widespread oxide mineral) and apatite (a common tracer mineral) in banded iron-formations (BIFs) are ideal minerals to study the hydrothermal and metamorphic processes. Shi et al. investigated the geochemical composition of modified magnetite and hydrothermal apatite, and in situ U-Pb geochronology on apatite from the Huogezhuang BIF-hosted Fe deposit, northeastern China. The chemical compositions recorded in modified magnetite and hydrothermal apatite from BIFs provide essential insights into the supernormal enrichment of iron during retrogressive metamorphism of BIFs. Apatite trace element composition as an indicator of ore deposit types: a machine learning approach https://doi.org/10.2138/am-2022-8805 Qiu et al. used machine learning to link the concentration variability of trace elements in apatite to the five most important types of ore deposits. However, machine-learning approaches are often considered a black box in that they may be too complex to be easily interpretable by humans. Their application of the machine-learning model, however, revealed that the trace elements thorium, uranium, europium, and neodymium in apatite are the most distinctive elements for the discrimination of different types of ore deposits and, thus, the results are easily applicable. Identifying serpentine minerals by their chemical compositions with machine learning https://doi.org/10.2138/am-2022-8688 Ji et al. introduce machine-learning algorithms called XGBoost and k-means to classify and cluster serpentine minerals based on the analysis of chemical composition datasets. As a complement to traditional geochemical methods, the machine-learning models are more effective in determining serpentine minerals. They also use a k-means model to show that the tectonic environment in which serpentine minerals form correlates with their chemical composition. Their models can be used to constrain the mass transfer and surrounding environments during the subduction of hydrated oceanic crust. Crystal habit (tracht) of groundmass pyroxene crystals recorded magma ascent paths during the 2011 Shinmoedake eruption https://doi.org/10.2138/am-2022-8765 Okumura et al. analyzed the shape variations due to combination of crystallographic faces (i.e., tracht) of groundmass pyroxene crystals in pumices from the 2011 eruption of Shinmoedake volcano, Japan. They also acquired tracht-specific crystal size distributions (CSDs) by scanning electron microscopy to obtain a more comprehensive view of the crystallization kinetics. They discuss the mechanism of the pyroxene tracht change and conclude that the tracht change resulted from a large degree of effective undercooling due to rapid decompression in the shallow conduit. Syneruptive magma ascent paths affect eruptive style, and the crystallization kinetics of groundmass crystals as small as nanolites provide clues to the conduit mechanisms controlling transitions in eruptive style. The findings reveal magma dynamics from a different perspective than conventional textures such as crystal number density and crystallinity. Reconstructing diagenetic mineral reactions from silicified horizons of the Paleoproterozoic Biwabik Iron Formation, Minnesota https://doi.org/10.2138/am-2022-8776 Duncanson et al. present petrographic observations, SEM, EMPA, and Raman spectroscopy from iron mineral phases preserved within silica-cemented horizons of the ~1.9 Ga Biwabik Iron Formation (Minnesota, USA) to constrain texturally early iron formation mineralogy from this crucial post-GOE (Great Oxidation Event) interval. Based on textural relationships, the iron silicate greenalite is identified as the earliest-forming iron silicate mineral preserved within silica-cemented horizons. The Mg- and Al-rich iron silicates chamosite and stilpnomelane are preserved proximal to fine-grained, non-silicified horizons, suggesting local geochemical exchange during early diagenesis. The presence of well-preserved, early-forming silicates containing predominantly ferrous iron may indicate reducing conditions at the sediment-water interface during deposition of the Biwabik Iron Formation. Future studies using iron silicate mineralogy as seawater geochemistry proxies should consider preservation by silica cementation, in addition to the effects of local geochemical exchange during diagenesis. Mannardite as the main vanadium-hosting mineral in black shale-hosted vanadium deposits, South China https://doi.org/10.2138/am-2022-8903 Yang et al. identified mannardite in the black shale-hosted vanadium deposits, which is the main vanadium-hosting mineral and provides 12.32% - 44.06% vanadium. The pentavalent vanadium species in seawater accumulated through organism activities may be reduced into quadrivalent vanadium by organic matter and then into trivalent vanadium species by H2S. Mannardite may be precipitated under the reductive condition with sufficient trivalent vanadium species, titanium (Ti) and biogenic barium (Ba). The results put forward new cognition on the occurrence states of vanadium, which shows mineralogical significance on understanding the metallogenic mechanism as well as beneficiation of vanadium in the black shale. Based on the proportion of vanadium from the mannardite (average of 24.95%), mannardite in the black shale-hosted vanadium deposits preserves a total of 19.6% vanadium in the world. Molybdenite-bearing vugs in microgranite in the preissac pluton, Quebec, Canada: Relicts of aqueous fluid pockets? https://doi.org/10.2138/am-2022-8770 Mulja and Williams-Jones demonstrated that (1) there exists rare occurrence of molybdenite-bearing miarolitic cavities in highly evolved fine-grained monzogranite dikes with •REE of 17.2, EuCN of 0.27 and Eu/Eu* of 0.24; (2) field, mineral-chemical, whole-rock composition, and stable isotope (O and S) data indicate a magmatic-hydrothermal origin for the cavities, molybdenite and other associated phases; (3) the cavities represent relicts of vapors (gas-fluid mixtures) that exsolved from an ascending felsic magma through fractures where it quenched as fine-grained monzogranite dikes; and (4) molybdenum that partitioned into the vapor phase precipitated as molybdenite in the cavities, where, based on volumetric relationships and thermodynamic data, it attained a maximum concentration of 7800 ppm. The equilibrium boundary of the reaction Mg3Al2Si3O12 + 3CO2 = Al2SiO5 + 2SiO2 + 3MgCO3 at 3-6 GPa https://doi.org/10.2138/am-2022-8696 The reaction between garnet and CO2 fluid is of interest because it constrains the stability of CO2 fluid in eclogites, whose minerals were found in the CO2-bearing diamonds. Vinogradova et al. determined the equilibrium boundary for the reaction Mg3Al2Si3O12 (Prp) + 3CO2 (F) = 3MgCO3 (Mgs) + Al2SiO5 (Ky) + 2SiO2 (Coe/Qz) over the pressure interval 3-6 GPa using a multianvil press. The established boundary crosses the graphite-to-diamond transition curve at 4.4 GPa and 1060 °C. Thus, the assemblage garnet + CO2 fluid is stable in the diamond stability field under P-T conditions of the continental geotherm with a heat flow of 40 mW/m2. Comment on Lee et al. (2022) “Reexamination of the structure of opal-A: A combined study of synchrotron X-ray diffraction and pair distribution function analysis” —Concerning opal https://doi.org/10.2138/am-2022-8863 Reply: On "Reexamination of the structure of opal-A: A combined study of synchrotron X-ray diffraction and pair distribution function analysis"—Reply to de Jong https://doi.org/10.2138/am-2023-9216