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 previous American Mineralogist Paper Highlights at https://msaweb.org/MSA/AmMin/notes/. 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 Interfacial interactions controlling adsorption of metal cations on montmorillonite https://doi.org/10.2138/am-2022-8834 Adsorption is one of the most remarkable properties of montmorillonite. However, our understanding of the interfacial interactions between metal cations and montmorillonite remains elusive, which has limited the insights into the migration, enrichment, and cycling of metals on Earth, and the evolution of montmorillonite itself and the changes of associated soil, and sediments. This paper by Li et al. examines the interfacial interactions for the adsorption of metal cations on montmorillonite and reviews the status on this research. Microstructural and compositional evolutions during transformation from biotite to berthierine: Implications for phyllosilicates alteration processes https://doi.org/10.2138/am-2023-8984 Using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive spectroscopy, and electron energy loss spectroscopy (EELS), Xi et al. identified a berthierine twin structure within weakly changed biotite in a rhyolite from Long Valley, California, USA. The nanoscale Fe-rich layers are composed of twinning berthierine layers rather than a single chlorite layer. The transformation of biotite to berthierine requires the dissolution of a tetrahedral (T) layer and the introduction of a new TO (O represents octahedral sheet) structure into the biotite stacking sequence, resulting in substituting one biotite layer (i.e., TOT) by two twinning berthierine layers (i.e., TO-OT). Morphological observations indicate that the transformation began at the biotite defect locations, concurrent with the rearrangement of metal cations. During the weak fluid reform of biotite, berthierine was produced via an interface-coupled dissolution-reprecipitation process. The EELS analyses further demonstrate that the Fe-rich biotite promotes the production of berthierine as the principal alteration product in low-temperature environments. This study also demonstrates that the combination of HAADF-STEM and EELS is effective for identifying nanominerals and elucidating their formation and alteration mechanisms. Vapor-phases as Cu transport agents for the shear-zone-hosted mineralization system: A perspective from H-O-S-Cu isotopes https://doi.org/10.2138/am-2022-8888 Elucidating metal transport agents is the key to understanding the genesis of deposits and tracking the locations of concealed orebodies. Zhao et al. demonstrate that integrating H-O-S-Cu isotopic analyses with geochemical modeling can reveal the vapor phase as the dominant metal transport agent in a metamorphic geological environment. From this perspective, metal precipitations can occur along the shear zone over a long distance because vapor phases can move outwards promptly. Their study provides a framework to track the locations of concealed orebodies for the shear-zone-hosted Cu deposits reliably. Don Juan Basin, Antarctica: A chemically altering environment with martian analog potential https://doi.org/10.2138/am-2022-8779 Foerder et al. present a coordinated geochemistry-, spectroscopy-, and mineralogy-based study of sediments from a basin in the McMurdo Dry Valleys of Antarctica with the purpose of investigating the type and degree of alteration occurring in and around a hypersaline and perennially liquid water pond found within. Sediment provenance, surface, and subsurface processes are also considered to provide information on alteration processes occurring in a cold, water-poor, Mars-like setting. The authors connect these geochemical and mineralogical observations to those detected at the martian surface to describe a possible analog setting (and process) for the formation of these ofttimes enigmatic aqueous, chemical alteration products on Mars. This work has important implications for the Hesperian to recent history of chemical alteration processes at and near the martian surface. High-pressure polymorphs of the ferroan dolomite: Possible host structures for carbon in the lower mantle https://doi.org/10.2138/am-2022-8737 Martirosyan et al. demonstrate a complex polymorphism of the dolomite-ankerite solid solutions at high pressure and a clear effect of cationic substitution on the phase behavior. Given the significant role of carbonates in the petrological and geochemical processes, such as carbonatitic melt formation, metasomatism, and red-ox reactions, the Dol-IIIc and IIIb polymorphs should be considered in the modeling of the lower mantle processes related to the deep carbon cycle. Revisiting the genesis of the adakite-like granitoids in collisional zones: water-fluxed melting of intermediate to felsic rocks with dilution by low Sr/Y phases https://doi.org/10.2138/am-2022-8873 Xie et al. investigated the origin of adakitic plutonic rocks through geochemical and textural characterization of rock-forming minerals in the orthopyroxene-bearing, Zhuyuan granodiorite (West Qinling, China). The study proposes that high Sr/Y signal is primarily controlled by the late-stage orthocryst assemblages (non-sieve textured plagioclase+ biotite + K-feldspar + quartz). The addition of low Sr/Y non-orthocrysts and associated melt may have diluted the primary “adakitic signal” in the magma reservoir, driving the bulk composition to more mafic values. The study also highlights that the high Sr/Y signal, which can be formed under various pressure conditions, is often controlled by source compositions. In this regard, many high Sr/Y adakitic granites cannot be directly used to infer the thickness of the continental crust when the source is a felsic to intermediate protolith melted under water-fluxed conditions. Pressure-induced phase transitions in Ni-bearing ferrosilite (Ni-En31Fs65) https://doi.org/10.2138/am-2022-8879 Metastable orthopyroxene is considered to be related to the stagnation of slabs due to its low density compared with other major slab minerals. Xu et al. observed three metastable phase transitions in Ni-bearing ferrosilite (Ni-En31Fs65) at 12.1(6) GPa, 15.6(6) GPa, and 31.3(25) GPa. This study revealed the possible phase transition path of Fe-rich orthopyroxene in extremely cold subducting slabs in the deep Earth: α-opx (Pbca) → β-opx (P21/c) → γ-opx (Pbca) → β-popx (P21ca). Thermoelastic properties of natural zircon: Non-metamict zircon https://doi.org/10.2138/am-2023-8986 Münchhalfen and Schreuer determined the thermoelastic properties and thermal expansion of natural single-crystal zircon without detectable radiation damage were in the temperature range between 100 K and 1650 K on five samples from Cambodia, Sri Lanka, and Tanzania. Their results are highly reproducible, allowing for a reliable extrapolation to 0 K. Previously unknown irreversible elastic effects were observed in the high-temperature range above 1500 K. Scheelite composition fingerprints pulsed flow of magmatic fluid in the Fujiashan tungsten skarn deposit, eastern China https://doi.org/10.2138/am-2022-8917 Skarn mineralization forms when magmatic fluids react with impure carbonate rocks. Scheelite is an important ore mineral in W skarns, and its chemical and isotopic composition reflects both the magmatic fluid and the reaction history of the fluid with the carbonate wall rocks. Ji et al. present cathodoluminescence images and in-situ trace element and Sr-O isotope data of scheelite from four stages of the hydrothermal skarn development in the Fujiashan W skarn deposit, i.e., scheelite in prograde and retrograde skarn, quartz-sulfide veins, and late calcite replacements. The results show that pulsed and restricted magmatic fluid flow produces zones with depletions in elements that partition strongly into scheelite and systematic changes of Sr and O isotope composition. Notably, chemical and isotopic variations in scheelite do not require the involvement of different fluids or changes in redox conditions. Mineralogy of the 1.45 Ga Wafangzi manganese deposit in North China: Implications for pulsed Mesoproterozoic oxygenation events https://doi.org/10.2138/am-2022-8919 The traditional view suggests that the presence of Mn(II) carbonates in manganese deposits was formed by the diagenetic reduction of precursor Mn(IV) oxides. Therefore, Precambrian sedimentary Mn deposits have been used to indicate the evolution of oxygen in Earth’s surface environments. However, recent studies have shown that these Mn(II) carbonates can directly accumulate within anoxic water columns, casting uncertainty on the robustness of using ancient Mn deposits to constrain the redox fabric of the past marine water columns. Based on the comprehensive mineralogical investigation of the Mesoproterozoic Wafangzi Mn-Fe deposit, Yan et al. suggest that the Mn(II,III)- and Fe(II)-bearing mineral phases were formed through the diagenetic reduction of primary Mn(IV) and Fe(III) minerals, supporting the traditional oxygenation metallogenic model. Together with contemporaneous Mn mineralization in western Australia, their study supports a continent-scale transient pulsed oxygenation event in the mid-Proterozoic oceans. Their findings shed light on the interaction between Mn cycles and oceanic redox environment in the critical “boring billion” earth history. Tourmaline growth in the border and wall zones of the Emmons Pegmatite (Maine, USA): Evidence for disequilibrium crystallization and boundary layer formation https://doi.org/10.2138/am-2023-8991 Van der Does et al. investigated unidirectional solidification textures and graphic intergrowths of tourmaline and quartz from the Emmons Pegmatite. Three textural groups were identified: comb-like tourmaline, quartz-tourmaline intergrowths (QTIs), and radiating tourmaline. Furthermore, five different morphologies were identified within these groups. Geochemical analyses show that the composition varies on three different scales: among the textural groups, intracrystalline, and within individual QTIs. The first two are explained by the progressive magmatic evolution of the dike and sector zoning, respectively. For the variations within the QTIs, the authors propose a model where the outer part of the QTI crystallizes from a water and flux-enriched boundary layer. The boundary layer forms as the central and first part of the QTI crystallizes. The skeletal part of the QTI then crystallizes from the boundary layer. These boundary layers have earlier only been observed in experimental studies, but this paper provides the first examples of boundary layers in natural samples. The fact that the geochemistry of the tourmaline varies on a millimeter to decimeter scale brings into question whether tourmaline in pegmatites can be used as a petrogenetic indicator for the bulk pegmatite melt. New Mineral Names https://doi.org/10.2138/am-2024-NMN10949