Editor’s Notes
Total Results: 1697
Volume 108 : June 2023 Issue
A shallow salt pond analog for aqueous alteration on ancient Mars: Spectroscopy, mineralogy, and geochemistry of sediments from Antarctica’s Dry Valleys
https://doi.org/10.2138/am-2022-8381
Understanding mineral formation on Mars is critical to understanding the planet's geochemical evolution, climate, and history of liquid water, as well as potential habitability. However, the formation processes behind mineral assemblages observed on Mars remain elusive. Here, Burton et al. examined aqueous alteration products developed in shallow sediments at a transient Antarctic brine pond as an example of the formation of clays, sulfates, and chlorides in extremely cold, water-poor, Mars-like settings.
Incorporation of chlorine in nuclear waste glasses using high-pressure vitrification: Solubility, speciation, and local environment of chlorine
https://doi.org/10.2138/am-2022-8599
Chlorine is one of the most important halogens involved in magmatic systems, representing a major troublesome element in the immobilization of nuclear waste, for which, however, there is a lack of fundamental understanding. Jolivet et al. investigated how chlorine dissolves in the structure of high-pressure borosilicate glasses using advanced spectroscopic techniques XPS and XAS. The speciation and the local environment of chlorine species have been determined and clarified. Furthermore, they propose an approach for predicting the chlorine solubility in a wide range of glass compositions.
Experimental constraints on miscibility gap between apatite and britholite and REE partitioning in an alkaline melt
https://doi.org/10.2138/am-2022-8535
Stepanov et al. performed synthesis of britholite and apatite from felsic melt, which showed that the addition of NaCl to the granite melt could have a pronounced effect on the behavior of REE. The change of the mineral association from monazite to apatite + britholite with the addition of NaCl illustrates the importance of halogens. REE entered the apatite structure via REE-Si substitutions. The results have implications for the interpretation of the phosphate associations in alkaline volcanic and plutonic rocks.
Thermal expansion of minerals in the tourmaline supergroup
https://doi.org/10.2138/am-2022-8580
The minerals in the tourmaline supergroup are widespread in Earth's crust, typically occurring in granites and granitic pegmatites, as well as in certain sedimentary and metamorphic rocks. In addition, tourmalines are the primary boron-bearing minerals in the earth. Tourmaline thermal-expansion data, therefore, are essential to the thermodynamic modelling not only of pegmatitic environments, but of all high-temperature B-rich mineral assemblages. Here, Hovis et al. provide an updated high-T dataset for the tourmaline mineral supergroup that will serve thermodynamic databases and will also be a valuable tool for better understanding tourmaline physical properties. Because present data demonstrate a similarity in thermal expansion among a wide variety of tourmaline compositions, there is the possibility of using end-member thermal expansion data for compositions that deviate significantly from those studied here.
Viscosity of Earth’s inner core constrained by Fe–Ni interdiffusion in Fe–Si alloy in an internal-resistive-heated diamond anvil cell
https://doi.org/10.2138/am-2022-8541
Diffusivity in iron alloys at high pressures and temperatures imposes constraints on transport properties of the inner core, such as viscosity. Because silicon is among the most likely candidates for light elements in the inner core, the presence of Si must be considered when studying diffusivity in the Earth's inner core. Park et al. conducted diffusion experiments under pressures up to about 50 GPa using an internal-resistive-heated diamond anvil cell (DAC) that ensures stable and homogeneous heating compared with a conventional DAC heating method and thus allows them to conduct more reliable diffusion experiments under high pressures. They determined the coefficients of Fe-nickel (Ni) interdiffusion in the Fe-Si 2 wt.% alloy. The upper limit of the viscosity of the inner core inferred from these results is low, indicating that the Lorentz force is a plausible mechanism to deform the inner core.
The distribution of carbonate in apatite: The environment model
https://doi.org/10.2138/am-2022-8389
The location of carbonate in the structure of carbonated apatite, the closest analog to the inorganic portion of bones and teeth, is of importance in the biological function of this compound, especially the possibility of the involvement of structural carbonate in acid-base regulation. Yoder et al. demonstrate that the environment model originally proposed by Fleet (2017) for apatites prepared at high temperature and pressure is also valid for apatites produced synthetically or biologically at ambient pressures and low temperatures. The model suggests that considerably more carbonate is sequestered in the apatite channel than was previously thought and brings a greater focus on the roles of both types of carbonate in the biological function of carbonate in bone mineral.
Low-temperature crystallography and vibrational properties of rozenite (FeSO4·4H2O), a candidate mineral component of the polyhydrated sulfate deposits on Mars
https://doi.org/10.2138/am-2022-8502
The current generation Mars Rovers use Raman spectroscopy to search for minerals that are thought to have formed early in the martian history, when Mars was able to sustain surface waters. Raman spectroscopy is a powerful analytical tool but relies on accurate fingerprint reference spectra to identify minerals. Meusburger et al. show that the Raman fingerprint of rozenite was misinterpreted in the literature and suggest a workflow for the construction of a reliable Raman spectroscopic database for planetary exploration.
Hydrothermal fluid signatures of the Yulong porphyry Cu-Mo deposit: Clues from the composition and U-Pb dating of W-bearing rutile
https://doi.org/10.2138/am-2022-8453
Rutile enriched in V, W, Mo, Sn and Sb can be used as a geochemical fingerprint of a hydrothermal fluid associated with mineralization. Chen et al. investigated the geochemical composition and U-Pb dates of hydrothermal rutile from the Yulong porphyry Cu-Mo deposit in east Tibet, China. The analysis of rutile crystals indicates that the patchy or sector zonation imparts a marked control on the distribution of W, which substitutes for Ti by a coupled substitution with the trivalent cations in the rutile. In situ LA-ICP-MS U-Pb dating shows that the age of the W-bearing rutile grains overlaps the previously reported molybdenite Re-Os ages and provides the ability to directly determine the age of the Cu-Mo mineralization. The mechanism of the enrichment of tungsten is effectively driven by the halogen-rich (F, Cl) aqueous fluids during hydrothermal mineralization in the Yulong deposit. Consequently, the chemical or isotopic composition recorded in rutile provides comprehensive information for better understanding of the nature of hydrothermal fluids during the deposition of porphyry deposits.
Magnetic contributions to corundum-eskolaite and corundum-hematite phase equilibria: A DFT cluster expansion study
https://doi.org/10.2138/am-2022-8584
Magnetic contributions to mixing phase diagrams are challenging to compute, yet may have significant impact on phase stability. Pope et al. develop a protocol that includes spin orientation as an additional configurational component within multi-component cluster expansions between magnetic and non-magnetic metal oxide alloys. Two systems are compared, one where magnetic contributions to the calculated phase diagram are inconsequential (corundum-eskolaite) and one where they are absolutely essential (corundum-hematite) to accurately determine the solvus.
Microchemistry and magnesium isotope composition of the Purang ophiolitic chromitites (SW Tibet): New genetic inferences
https://doi.org/10.2138/am-2022-8392
Xiong et al. investigated the textural and compositional characteristics of silicate sulfide and exotic UHP-SuR mineral inclusions in Purang ophiolitic chromitite grains, suggesting a complex evolution of this Jurassic ophiolitic massif in SW Tibet. Evolution of these rocks included subduction of lithospheric slabs into the transition zone, crystallization of magnesiochromite and some massive chromitite at depth, incorporation of UHP and highly reduced phases into the chromitites, and entrapment of oceanic lithospheric slabs in a supra-subduction zone (SSZ) setting, where they undergo varying degrees of reaction with hydrous, SSZ melts.
Pyrite geochemistry in a porphyry-skarn Cu (Au) system and implications for ore formation and prospecting: Perspective from Xinqiao deposit, Eastern China
https://doi.org/10.2138/am-2022-8527
Xiao et al. investigated the geochemistry of pyrite in a porphyry-skarn Cu (Au) system in Xinqiao deposit, eastern China. Geological, trace element and S isotope analyses show that the colloform pyrite formed during early skarn mineralization. Colloform pyrite was produced by rapid decompression that triggered fluid boiling and cooling when the Cretaceous magmatic-hydrothermal fluid flowed along the Devonian-Carboniferous unconformity. Stratabound sulfide ore is sourced from Cretaceous magmatic-hydrothermal fluids, and formed from multi-stage magmatic-hydrothermal pulses. Co and Ni in pyrite increase towards porphyry and skarn ore, whereas As, Sb, Pb, Ag and Bi are enriched in pyrite in distal stratabound ore. The results indicate pyrite chemistry can be effective in discriminating the genesis of different deposit types related to porphyry-skarn systems and can potentially be used as a vectoring tool during exploration in the MLYB and elsewhere.
UV/Vis single-crystal spectroscopic investigation of almandine-pyrope and almandine-spessartine solid solutions: Part I. Spin-forbidden Fe2+,3+ and Mn2+ electronic-transition energies, crystal chemistry, and bonding behavior
https://doi.org/10.2138/am-2022-8499
Investigation of the solid-solution behavior of aluminosilicate garnets is a long, continuing work in progress and much still needs to be studied. A fundamental problem is to understand the nature of local structural heterogeneity that arises through the exchange of different atoms of varying sizes and electronic properties. Geiger et al. measured natural almandine-pyrope, {Fe2+3x,Mg3-3x}[Al2](Si3)O12, and almandine-spessartine, {Fe2+3x,Mn2+3-3x}[Al2](Si3)O12, crystals using UV/Vis/NIR (~29000 to 10000 cm-1) optical absorption spectroscopy. The spectra and changes in energy of a number of Fe2+ and Mn2+ spin-forbidden electronic transitions were analyzed as a function of garnet composition across both binaries in order to understand the underlying bonding behavior.
Single-crystal UV/Vis optical absorption spectra of almandine-bearing and spessartine garnet: Part II. An analysis of the spin-forbidden bands of Fe2+, Mn2+, and Fe3+
https://doi.org/10.2138/am-2022-8500
Almandine and spessartine are common occurring aluminosilicate garnets with the ideal end-member crystal-chemical formulas {Fe2+3}[Al2](Si3)O12 and {Mn2+3}[Al2](Si3)O12. Garnet is a remarkable phase in several ways and much research in the Earth Sciences has focused on the different rock-forming species. Taran et al. demonstrate that a crystal-chemical aspect of significance is the eight-fold or triangular dodecahedral coordination of Fe2+ (d6) and Mn2+ (d5) by oxygen anions and the various physical properties arising from this. Different types of electronic transitions in garnet, as expressed in the NIR/Vis/UV regions of the electromagnetic spectrum, can result from the Fe2+ and Mn2+ cations. The transitions can be studied by optical absorption spectroscopy, which yields information on chemical bonding.
Single-crystal UV/Vis absorption spectroscopy of aluminosilicate garnet: Part III. {Fe2+} + [Fe3+] → {Fe3+} + [Fe2+] intervalence charge transfer
https://doi.org/10.2138/am-2022-8756
The various intervalence charge transfer (IVCT) mechanisms that can occur in silicate garnets, with a general crystal-chemical formula {X3}[Y2](Z3)O12, are not fully understood. Geiger and Taran conducted spectroscopic measurements on aluminosilicate garnets, with a focus on understanding IVCT behavior in almandine-rich, spessartine-rich and grossular-rich crystals and one intermediate composition almandine-pyrope garnet. The authors also reviewed and analyzed various possible IVCT mechanisms in both Ca-Ti-bearing and aluminosilicate garnets. The goal is to achieve a better and more complete understanding of the electronic transition behavior of an important rock-forming mineral group.
A novel method for experiments in a one-atmosphere box furnace
https://doi.org/10.2138/am-2022-8867
This letter by Linzerova et al. presents a new high-temperature experimental method for one-atmosphere box furnace, utilizing commercially available low-cost materials. The method was designed to facilitate textural analysis of voluminous samples, with no need to use noble-metal capsules.
Volume 108 : May 2023 Issue
Eu speciation in apatite at 1 bar: An experimental study of valence-state partitioning by XANES, lattice strain, and Eu/Eu* in basaltic systems
https://doi.org/10.2138/am-2022-8388
Tailby et al. describe three new redox calibrations for apatite in basaltic systems. The first calibration includes a methodology that uses the intensity of a negative Eu anomaly relative to neighboring Sm and Gd. The second measures the intensity of the negative Eu anomaly relative to the lattice strain. The third employs a direct XANES measurement on the Eu L3 XANES spectral features.
The effect of composition on chlorine solubility and behavior in silicate melts
https://doi.org/10.2138/am-2022-8450
Thomas and Wood used a sliding chlorine buffer (a mixture of AgCl/AgI and Ag) to determine the fugacities (and activities) of chlorine in many silicate melts. They show that for a wide range of compositions, from basalt, phonolite, andesite, dacite, and rhyolite that Henry's Law is obeyed for the Cl contents of interest in natural volcanic systems. They quantified the effects of different oxides, CaO, FeO, etc., on Cl solubility and determined conditions of NaCl saturation at high pressure and temperature.
High-temperature phase relations of hydrous aluminosilicates at 22 GPa in the AlOOH-AlSiO3OH system
https://doi.org/10.2138/am-2022-8429
Aluminous hydrous phases are key minerals for understanding the Earth's deep water cycle since they have been found as inclusions in superdeep diamonds. In this study, Takaichi et al. investigated the phase relations of hydrous aluminosilicates under pressure conditions corresponding to Earth's interior. They found the formation of two unknown hydrous aluminosilicates. These results indicate that various hydrous aluminosilicates can widely exist within subducting crustal materials in the mantle transition zone to the lower mantle.
Crystallization of spinel from coexisting silicate and sulfide immiscible liquids: An equilibrium case with postcumulus reactions
https://doi.org/10.2138/am-2022-8473
Mao et al. find that the Kalatongke deposit is an example of where the same mineral phase from two immiscible liquids exhibits approximately equivalent compositions.They determined that the chalcophile element concentration in Cr-magnetite/magnetite of magmatic Ni-Cu deposits results from element exchange with the coexisting sulfide melt, and that the texture and composition of spinel may serve as an indicator for not only the compositional evolution of silicate/sulfide melts but also the percolation and enrichment history of sulfide liquid.
X-ray absorption spectroscopy study of Mn reference compounds for Mn speciation in terrestrial surface environments
https://doi.org/10.2138/am-2022-8236
Zahoransky et al. analyzed a broad range of inorganic and organic Mn compounds by bulk Mn K-edge X-ray absorption spectroscopy (XAS); they evaluated the accuracy of XAS to quantify Mn oxidation states, and explored spectral similarities between and within different Mn species groups. Their study provides the first comprehensive framework for the analysis and interpretation of bulk Mn XAS spectra of natural samples and, thus, for understanding the role of Mn in environmental processes.
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