American Mineralogist February 2026 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 feature is available to anyone who registers on the site. Thank you for reading American Mineralogist. Sincerely, Paul Tomascak Fabrizio Nestola Editors, American Mineralogist American Mineralogist Volume 111; Number 2; 02-01-2026 Seismic signature of the upper continental crust: Implications from the thermoelastic properties of liebermannite and K-hollandite II Dong Wang, Longyu Duan, Xin Deng, Wenzhong Wang, Zhongqing Wu Wang et al. investigate what Upper Continental Crust (UCC) will be like in Earth's deep interior, focusing on two key minerals: liebermannite and K-hollandite II. The study used advanced calculations to understand their properties under extreme mantle conditions. Combining this information with mineral compositions of UCC, they created profiles showing the density and velocity of UCC within the Earth. Notably, UCC accumulates at the bottom of the mantle transition zone due to a density crossover with the surrounding mantle. At the top of the lower mantle, UCC undergoes a transition from high-velocity to low-velocity, marked by strong directional differences (anisotropy). The shift from liebermannite to K-hollandite II contributes to significant velocity changes. These variations may explain observed high-velocity anomalies beneath collision zones of continents and strong anisotropy around low-velocity anomalies in the upper lower mantle. Importantly, after garnet breaks down in UCC, it becomes challenging to distinguish UCC from oceanic crust due to similar velocities. The study provides insights into the intricate behaviors of UCC within Earth's interior, helping to understand phenomena like high-velocity anomalies and anisotropy observed in specific geological zones. https://doi.org/10.2138/am-2024-9562 Arsenohauchecornite, ognitite, parkerite, and related minerals from Onça Rosa orebody, Carajás, Brazil: Fingerprinting PGE signatures in hydrothermal Ni ores Yuri Campo Rodriguez, Cristiana Ciobanu, Nigel Cook, Ashley Slattery, Benjamin Wade, Sarah Gilbert, Maria Schutesky, Kathy Ehrig This study describes mineral assemblages in nickel-rich sulfide mineralization from the Onça Rosa orebody. Rare accessory Ni-Bi-minerals observed include arsenohauchecornite, ognitite (second world occurrence), and parkerite. Nanostructures in pentlandite reveal fluid pathways and host Pt-Ag-Bi-Te phases as nanoparticles. The presence of Pd and Pt extends the potential for PGE in hydrothermal Ni-sulfide ores in the Carajás Domain, a finding with implications for exploration in the region. https://doi.org/10.2138/am-2024-9647 Scandio-fluoro-eckermannite, NaNa2(Mg4Sc)(Si8O22)F2, a new Sc-dominant amphibole-supergroup mineral from the Bayan Obo deposit (China) Shuang-Liang Liu, Hong-Rui Fan, Xiangping Gu, Hai-Dong She, Kui-Feng Yang, Xiao-Chun Li, Qi-Wei Wang, Zhan-Feng Yang, Yonggang Zhao, Fenggang Wang, Xuan Liu A new Sc-dominant amphibole-supergroup mineral has been discovered in the Bayan Obo REE-Nb-Fe polymetallic deposit, China. The ideal formula of the mineral is NaNa2(Mg4Sc)(Si8O22)F2, and it has been named scandio-fluoro-eckermannite. Both the mineral and its name have been approved by the IMA-CNMNC (2024-002). The discovery of scandio-fluoro-eckermannite highlights the importance of amphibole in controlling Sc in this type of ore-forming system. Scandio-fluoro-eckermannite might also be used as a potential recorder to investigate the enrichment process of Sc in the Bayan Obo deposit. https://doi.org/10.2138/am-2024-9667 Investigating the formation and enrichment processes of the super-large North Sanshandao gold deposit (Jiaodong Peninsula, Eastern China): An in-depth mineralogical perspective Jian Li, Zhiming Yang, Mingchun Song, Leilei Dong, Wenyan Cai, Ming Lei, Qingyi Cui This study investigates the mechanism of visible gold and high-grade ore zones of the large North Sanshandao gold deposit. Through in-depth analysis of in situ LA-ICP-MS trace element and LA-MC-ICP-MS sulfur isotope on various pyrite generations, these findings are of importance to the field of Jiaodong gold deposits. This study provides a new model for the widespread development of over 80% of the disseminated-type mineralization in the Jiaodong Peninsula, emphasizing Au remobilization (via coupled dissolution-reprecipitation process) as a key factor for the formation of high-grade and high-tonnage ore zones, and sheds new light on the multistage ore-material enrichment in large-scale gold mineralization (storage of sulfur may have been pre-enriched before mineralization). https://doi.org/10.2138/am-2024-9701 Fe2+/Fe3+ Intervalence Charge Transfer and Enhanced d-d Absorption in Mixed Valence Iron Minerals at Elevated Temperatures Helen Evans, George Rossman A broad range of mixed valence Fe minerals are found to become much more optically transparent at elevated temperatures due to phenomena related to interactions between Fe2+ and Fe3+ cations: their Fe2+/Fe3+ intervalence charge transfer absorption bands lose significant intensity, as can their Fe2+ d-d absorption features, which are likely enhanced by Fe2+/Fe3+ exchange-coupled pairs. This behavior has potential implications for the importance of radiative conductivity in the Earth's mantle. https://doi.org/10.2138/am-2024-9724 Controls on Metal Zonation in Porphyry-Skarn Systems: Evidence from the Tonglvshan Cu Polymetallic Deposit, Eastern China Xiaolin Wu, Guiqing Xie, Jing Xu, Wenyuan Liu Pyrite and sphalerite are the most widely distributed sulfides in the porphyry-skarn system, and their trace elements and sulfur isotopes record variations in spatio-temporal zoning and ore-forming environments. In the early stage, pyrite shows an increasing trend in Co, Ni, As, and Se concentrations with distance from the intrusion, but exhibits depletion in the most distal vein-type ore. This variation pattern contrasts with those observed in other similar porphyry-skarn deposits in the MLYRB and is recorded by the Se-Co/As ratio. This suggests that redox conditions are the primary controlling factor, with temperature playing a secondary role. In contrast, the spatial variations in sulfur isotopes in pyrite are primarily controlled by temperature. Late-stage sphalerite displays spatial trends, evolving from high Fe, Co, and Mn contents in skarn-type ores to higher Cd, Hg, and Sn concentrations in carbonate-replacement-type and distal vein-type ores. These trends are also influenced by redox and temperature differences, as recorded by the Mn/Sn-Fe/Cd ratios. These sulfide compositional characteristics may provide valuable insights into the mineralization processes of other similar porphyry-skarn deposits. https://doi.org/10.2138/am-2024-9726 Anomalously high REE diaspore formed in bauxite overlying paleokarstic surface Lei Liu, Yongbo Peng, Xuefei Liu, Qingfei Wang, Xuefei Sun, Lihua Zhao, Wenxia Wang, Rongrong Liang, Jun Deng pH conditions and leaching control the distribution and enrichment of REE in bauxite of the Benxi Formation (North China Craton). REE are enriched mainly by the substitution of Al3+ in the crystal lattice of diaspore, which is identified as the principal REE host. Variations in REE occurrence among diaspore, anatase, kaolinite, hematite, and goethite reflect the combined influence of mineral crystal structure and formation processes. https://doi.org/10.2138/am-2025-9748 New minerals auropolybasite [Ag15AuSb2S11] and auropearceite [Ag15AuAs2S11]: Implications for the formation of bonanza ores in epithermal systems Tomáš Mikuš, Juraj Majzlan, Jozef Vlasáč, Jakub Plasil, Jiří Sejkora, Martin Stevko, Vaclav Petricek, Emil Makovicky Auropolybasite (IMA 2024-006) and auropearceite (IMA 2024-025), the new members of the polybasite-pearceite group are presented from the bonanza-type Ag-Au epithermal mineralization in Western Carpathians (Slovakia). Ore is significantly depleted in Cu, leading to an extraordinary Cu-free mineral assemblage. The main aspect of these minerals lies in the incorporation of gold into their structure, and the authors confront this finding with previous research on polybasite-pearceite group minerals. Besides a fundamental description of crystallography and crystal structure, the complicated problem of twinning in these minerals is interpreted, and the essential gold for silver substitution is explained. Moreover, the role of gold in known sulfides and sulfosalts is discussed. Finally, there are implications for the fluid properties responsible for the genesis of these minerals in epithermal deposits. https://doi.org/10.2138/am-2025-9806 Incongruent melting of garnet during garnet-spinel transition and its implication to the lithospheric exhumation Dongya Zou, Anping Chen, Hongdan Deng, Xiaoyan Gu, Hongfu Zhang, Huiting Zhang, Yan Tao Hao Phase transitions with strong rock density influences play an important role in the vertical surface movement of the Earth. Garnet-spinel transition leads to a moderate decrease in the density of the lithospheric mantle, resulting in the syn-rift uplift in the extending lithosphere. The transition processes of garnet-spinel, however, remain unclear. Zou et al. analyzed the mineral chemistry of spinel-pyroxene symplectites around garnet from an olivine-websterite xenolith hosted by the Cenozoic Xilinhot basalts in northeast China. This work provides the first physical evidence of incongruent melting of garnet during the garnet-spinel transition and provides a rare case to connect the phase transition and lithospheric exhumation. https://doi.org/10.2138/am-2025-9809 Quartz-petalite intergrowths in the Yichun pegmatite: Formation from late-stage Li-rich melts and implications for Li mineralization in rare-metal granites Mingqian Wu, Iain Samson, Anouk Borst, Xi Diao, Charles Beard, Xu Zheng, Mei Fan, Zhao-Liang Hou, Kunfeng Qiu Whether Li in peraluminous rare-metal granites was concentrated to economic grades solely by igneous processes or, in part, by metasomatic processes is still under debate. The Yichun deposit is a suitable locality to address this debate. Wu et al. concluded that more than half of the economic grades of Li in the topaz-lepidolite granite at Yichun were contributed through metasomatism after a magmatic concentration. https://doi.org/10.2138/am-2025-9818 The optics of a possible new interference figure in mineralogy Isaac Oliveira, Laryssa Carneiro, Lee Groat, Lucilene Dos Santos, Carlos Paschoal, Tereza Neri Likely a new type of interference figure: grossular garnets collected in Quixeramobim city in Brazil exhibit a new interference figure, called the "mosaic," observed in seven samples of this garnet variety. The "mosaic" is formed by the agglutination of colors (blue, yellow, and purple) when viewed with the quartz-gypsum accessory plate, due to the different light vibration directions as it passes through these anisotropic garnets. The "mosaic" configuration occurs when the optic axes and acute and obtuse bisectrices align in such a way that both inclined (//) and perpendicular (⟂) directions are present simultaneously. So far, the "mosaic" has only been observed in garnets of the grossular group from Quixeramobim (Brazil) and occurs only in minerals that exhibit a high degree of optical disorder. https://doi.org/10.2138/am-2025-9824 The first meteoritic ammonium mineral: Discovery of boussingaultite in the Orgueil CI1 carbonaceous chondrite Sergey Britvin, Oleg Vereshchagin, Natalia Vlasenko, Maria Krzhizhanovskaya, Marina Ivanova, Irina Volkova The paper reports the discovery of the first meteoritic ammonium mineral, nickeloan boussingaultite, (NH4)2(Mg,Ni)(SO4)2·6H2O. The mineral was found in Orgueil, a primitive carbonaceous chondrite closely related to the carbonaceous asteroids Ryugu and Bennu. It is demonstrated that boussingaultite (ammonium Tutton's salt) may serve as the likely carrier of bound ammonia in cometary and asteroidal bodies. https://doi.org/10.2138/am-2025-9851