Phyllosilicate Minerals Research Articles

A one‐pot biosynthesis of an aerogel composite based on attapulgite clay/bacterial cellulose to remove Pb 2+ ion

A one‐pot biosynthesis of an aerogel composite based on attapulgite clay/bacterial cellulose to remove Pb ²⁺ ion

Mechanical zonation of rock properties and the development of fluid migration pathways: implications for enhanced geothermal systems in sedimentary-hosted geothermal reservoirs

Oil and gas operations in sedimentary basins have revealed the occurrence of significant temperature anomalies at depth, raising the possibility of major geothermal resource potential in the sedimentary sequences. The efficient development of such a resource may require enhancement by hydraulic stimulation. However, effective stimulation relies on an initial assessment of in situ mechanical properties and a model of the rock response. Here, we examine the distribution of mechanical properties (unconfined compressive strength, UCS; ultrasonic velocity-derived Poisson ratio, ν; and, scratch toughness, Ks) along the cored interval of a sedimentary formation with a known low-to-medium temperature geothermal anomaly in the Permian Basin, U.S. Our results reveal the presence of mechanical stratigraphy along the core, demonstrated by the alternation of distinct soft–hard (i.e.,less stiff-to-stiff) mechanical zone couplets composed of: (1) mechanically softer 0.17-m-thick Zone-A and 0.18-m-thick Zone-C with mean values of UCS = 110 MPa, ν = 0.25, Ks = 1.89 MPa·√m; and (2) mechanically harder 0.41-m-thick Zone-B and 0.15-m-thick Zone-D which show mean values of UCS = 166 MPa, ν = 0.22, and Ks = 2.87 MPa·√m. Although X-ray diffraction analyses of the samples suggest that the entire rock matrix is dominated by dolomite, the harder zones show an abundance of quartz cement (> 30%) and relatively lower phyllosilicate mineral content (< 2%) than the softer zones. Further, we observe that the mechanically harder zones have the greatest occurrences and thicknesses of hydrothermal alterations (anhydrite veins and nodules), indicating that the rock had experienced hydrothermal fluid circulation (basinal brines) in the past. We infer that the mechanical stratigraphy most likely influenced the spatial clustering of fractures that facilitated hydrothermal fluid migration in the past, and provides insight that is relevant for the exploitation of geothermal energy resources in sedimentary basins. We suggest that the harder zones or formation intervals with higher ratios of the hard zones relative to soft zones represent viable targets for hydraulic stimulation of a sedimentary-hosted geothermal reservoir, both for the emplacement of new fractures and the linkage of pre-existing fractures to allow efficient fluid circulation. Our findings in this study provide insight that is relevant for understanding the complexity of pre-existing mechanical heterogeneity in sedimentary-hosted geothermal reservoir targets in other places.

Developing Atom Probe Tomography of Phyllosilicates in Preparation for Extra‐Terrestrial Sample Return

Hydrous phyllosilicate minerals, including the serpentine subgroup, are likely to be major constituents of material that will be bought back to Earth by missions to Mars and to primitive asteroids Ryugu and Bennu. Small quantities (&lt; 60 g) of micrometre‐sized, internally heterogeneous material will be available for study, requiring minimally destructive techniques. Many conventional methods are unsuitable for phyllosilicates as they are typically finely crystalline and electron beam‐sensitive resulting in amorphisation and dehydration. New tools will be required for nanoscale characterisation of these precious extra‐terrestrial samples. Here we test the effectiveness of atom probe tomography (APT) for this purpose. Using lizardite from the Ronda peridotite, Spain, as a terrestrial analogue, we outline an effective analytical protocol to extract nanoscale chemical and structural measurements of phyllosilicates. The potential of APT is demonstrated by the unexpected finding that the Ronda lizardite contains SiO‐rich nanophases, consistent with opaline silica that formed as a by‐product of the serpentinisation of olivine. Our new APT approach unlocks previously unobservable nanominerals and nanostructures within phyllosilicates owing to resolution limitations of more established imaging techniques. APT will provide unique insights into the processes and products of water/rock interaction on Earth, Mars and primitive asteroids.

The relationship between the geochemical and mineralogical characteristics of Calcocambisol, colluvium and recent marine lake sediment of the narrow seashore intertidal zone: a case study from the Veliko Jezero (Mljet Island, Croatia)

This study investigates the mineral composition, particle size distribution and geochemical characteristics of Calcocambisol, colluvium and recent marine lake sediment in a narrow intertidal seashore zone of the Veliko Jezero on the Island of Mljet (Croatia). The obtained results show that the fractions of Calcocambisol/colluvium less than 2 mm and 2 µm display similar particle size distribution (PSD) curves compared to marine lake sediments containing larger particles in these fractions. The smallest fractions of the investigated materials that are less than 1 µm show identical PSD curves. The bulk and clay mineral composition of the marine lake sediment show that the non-carbonate fraction is derived from weathering of the surrounding soils and colluvium containing quartz, feldspars and phyllosilicates (illitic material, kaolinites, chlorite, and a mixed-layer clay mineral, MLCM), as well as the authigenic formation of early-diagenetic pyrite, while one part is related to the yield of material by aeolian deposition (amphibole). The observed difference between the phyllosilicate mineral phases in the clay fraction of the Calcocambisol/colluvium and the carbonate-free clay fraction of the marine lake sediment is related to 1) the presence of chlorite in the marine lake sediment and 2) the higher content of MLCM in the Calcocambisol/colluvium. The chlorite in the marine lake sediment was inherited from the Calcocambisol/colluvium as a result of soil erosion prior to its complete destabilization in the soil. High Chemical Index of Alteration (CIA) values in the Calcocambisol and colluvium clearly indicate their intense weathering. Based on the Sm/Nd and Ti/Al ratios, it can be concluded that the aluminosilicates in the Calcocambisol, colluvium and marine lake sediment are of the same provenance. The distribution of each analysed element among the sequential fractions is very similar in both the Calcocambisol and colluvium. The highest concentrations for most of trace elements in the Calcocambisol, colluvium and marine lake sediment was determined in their residual fraction. Mn, Co and Pb show a different partitioning between the Calcocambisol/colluvium and marine lake sediment, respectively.

Influence of CaO/FeO ratio on the formation mechanism and properties of alkali-activated Fe-rich slags

In the search for CO2 mitigating cement technologies, alkali-activated Fe-rich slags present a possible alternative. The influence of the chemical composition of the synthetic Fe-silicate slag on the reaction mechanisms is assessed by varying the CaO/FeO molar ratio. The alkali-activated Fe-rich slags consist of trioctahedral layers that are shown to be hydroxylated and in contact with silicates, in a similar way to phyllosilicate minerals. The formation of this phyllosilicate-like structure is hindered during the first days for samples with high CaO/FeO ratios, because of the partial incorporation of Ca in the trioctahedral layers. At later ages, the samples with higher CaO/FeO ratios gain in reaction extent, to exceed the reaction extent of low CaO/FeO ratios at 28 days and beyond. The increase in compressive strength is even more pronounced than the effect on the reaction extent, which underlines the importance of Ca on the inherent strength of the binding phases.

Montmorillonite-Based Two-Dimensional Nanocomposites: Preparation and Applications.

Montmorillonite (Mt) is a kind of 2:1 type layered phyllosilicate mineral with nanoscale structure, large surface area, high cation exchange capacity and excellent adsorption capacity. By virtue of such unique properties, many scholars have paid much attention to the further modification of Mt-based two-dimensional (2D) functional composite materials, such as Mt-metal hydroxides and Mt-carbon composites. In this review, we focus on two typical Mt-2D nanocomposite: Mt@layered double hydroxide (Mt@LDH) and Mt@graphene (Mt@GR) and their fabrication strategies, as well as their important applications in pollution adsorption, medical antibacterial, film thermal conduction and flame-retardant. In principle, the prospective trend of the composite preparation of Mt-2D nancomposites and promising fields are well addressed.

The effect of porewater ionic composition on arsenate adsorption to clay minerals

Adsorption of arsenate on clay minerals can control the partitioning and mobility of arsenic and subsequent contamination of groundwater. While the effect of ionic strength on arsenic adsorption to phyllosilicate minerals has been evaluated for various clay minerals, the specific ionic composition of the surrounding porewater can play a critical role in promoting adsorption (or desorption) of arsenate (HxAsO4x-4). We conducted a series of adsorption isotherms to evaluate the adsorption of arsenate to various phyllosilicates in the presence of monovalent (K+), divalent (Mg2+, Ca2+), and trivalent (La3+) cations while maintaining constant ionic strength and pH. Adsorption isotherms were combined with surface complexation modeling to examine retention processes of arsenate as a function of ionic composition in the surrounding solution. The higher charge density of greater valent cations results in stronger outer-sphere bridging complexes between negatively charged phyllosilicate mineral surfaces and negatively charged arsenate oxyanions. Higher valent cations thus enhance the propensity for arsenate adsorption on phyllosilicate minerals. We further deciphered surface complexation processes by conducting adsorption isotherms on various clay minerals including smectite, illite, and pyrophyllite to evaluate the role of interlayer, permanent charge, and terminal edge sites. We conclude that arsenate is most likely retained largely on the planar surface where structural negative charge emanates allowing cation bridging complexes to develop. Our findings illustrate that clay mineralogy of soils and sediments can combine with porewater ionic composition (and specifically the proportion of divalent cations) to describe arsenic transport, particularly in iron- or aluminum-oxide poor systems.

Interaction of Soil Microbes with Organoclays and their Impact on the Immobilization of Hg under Aerobic Conditions

Immobilization of mercury (Hg) leaching from bank soils of East Fork Poplar Creek (EFPC) is considered part of remediation strategies to mitigate the amount of Hg entering the creek. Different approaches are currently being evaluated, such as utilizing engineered sorbents to immobilize Hg species in EFPC bank soils. However, the influence of environmental microbes on the immobilization of Hg by sorbents is unknown. Organocation-modified phyllosilicate clay minerals (organoclays) are widely used as sorbents for the immobilization of contaminants. This study evaluates the interactions of Serratia marcescens and Burkholderia thailandensis with the sorbent Organoclay PM-199 and their impact on the immobilization of Hg under aerobic conditions. We evaluated the competitive binding of Hg between sorbents and selected microorganisms in a series of pure culture studies using bacterial strains identified in EFPC bank soil samples. Our results suggest that Hg sorption by Organoclay PM-199 is not significantly impacted by common soil bacteria present in EFPC, specifically Serratia marcescens and Burkholderia thailandensis, which are known to form biofilms. These findings suggest that sorbent amendments are an effective strategy for the remediation of Hg contamination in natural ecosystems.

Effects of lithofacies on pore system evolution of storm-wave silt-rich fine-grained sediments. Early Silurian Qusaiba Member (Qaliba Formation), NW Saudi Arabia

Storm-wave sediments are considered a potential unconventional resource in the Middle East region, i.e., the early Silurian Qusaiba Member of the Qaliba Formation in Saudi Arabia. Extremely few studies have examined the controls of lithofacies heterogeneity on pore types, sizes, distribution, and connectivity. Therefore, this study intended to illustrate lithofacies controls on pore systems using various integrated approaches. Based on lithofacies analysis, seven lithofacies were identified and interpreted as storm-wave-dominated distal, medial, and proximal shelf deposits. The results of this study reveal two main types of pore systems: interparticle and intraparticle pores, which have been thoroughly recongized across all recognized lithofacies. Nuclear magnetic resonance (NMR) data showed positively and negatively skewed bimodal porosity distribution curves in the proximal and distal shelf lithofacies, respectively; however, the NMR data of medial shelf lithofacies were found to be normally distributed with unimodal distribution curves. Phyllosilicate minerals associated with interparticle pores (≤1 μm) were observed in the distal lithofacies; however, larger-scale interparticle pores were observed in both medial and proximal lithofacies. Such variation was also reflected in the NMR curves, resulting in negatively and positively skewed distribution curves of T2. Diagenetic facies (i.e., calcite, phosphate, pyrite, iron oxides, and clay minerals cementations) occurred during syndepositional, early, and intermediate burial stages before oil generation window. This study facilitates the understanding of the impacts of lithofacies and diagenetic facies on the pore system, and, the petrophysical characteristics of mudrocks in similar depostional settings.

Clay mineralogical evidence for mid-latitude terrestrial climate change from the latest Cretaceous through the earliest Paleogene in the Songliao Basin, NE China

From the latest Cretaceous (late Campanian to Maastrichtian, ~76-66 Ma) through the earliest Paleogene, changes of greenhouse climate were linked to catastrophic geological events and massive biotic extinction and were primarily derived from marine records. Here we present a high-resolution, tightly age-constrained, clay mineralogical record from the Sifangtai and Mingshui formations of the terrestrial Songliao Basin, northeast China. Smectite and illite are the dominant clay species and are derived from the weathering of parent rocks and/or pedogenesis in paleosols. We use the percentage ratio of smectite and illite, the illite chemistry index, and the percentage ratio of phyllosilicate clay minerals and quartz in clay fractions for paleoclimatic reconstruction. Our results show that from the latest Cretaceous through the earliest Paleogene, values of all three clay mineralogical proxies in the Songliao Basin are generally higher during warming intervals than those during cooling intervals. This dataset suggests that warming caused strengthened moisture delivery from the Pacific, increasing precipitation and intensified chemical weathering, whereas cooling was accompanied by increasing dryness and physical weathering. Across the Cretaceous-Paleogene boundary, the warming likely related to Deccan volcanism, the transient cooling afterwards, and the warming in the earliest Paleogene are characterized by changes in the illite chemistry index and paleosol carbonate stable isotopic excursions as shown in previously published records, reflecting fluctuations in hydroclimate and weathering intensity. Our work demonstrates that terrestrial climate and weathering intensity in the mid-latitude Songliao Basin fluctuated during the latest Cretaceous through the earliest Paleogene and sensitively responded to global climate changes.

Recommendations for offline combustion-based nitrogen isotopic analysis of silicate minerals and rocks.

Due to isotope fractionations during partial nitrogen release from minerals and rocks, the complete extraction of nitrogen for analysis is crucial to ensure high-quality nitrogen isotopic data. However, the appropriate nitrogen extraction conditions (e.g. temperature, duration) have not been established for most silicate minerals and rocks. Nitrogen in a number of common minerals and rocks was extracted using the most robust sealed-tube offline combustion techniques, purified and quantified in a custom-made metal manifold, and carried by helium gas to an isotope ratio mass spectrometer for isotopic measurement at nanomolar nitrogen level. Each mineral or rock was combusted in a variety of temperature and duration conditions to compare the nitrogen yields and isotopic compositions. The nitrogen yields and isotopic compositions of minerals and rocks are strongly affected by combustion temperature and duration. The optimal combustion temperature is lowest for cyclosilicate minerals, followed by phyllosilicate, tectosilicate and inosilicate minerals. Preheating of samples can induce significant nitrogen loss and δ15 N shift. Heating of samples above their optimal temperatures may cause nitrogen re-assimilation by the residual mineral or rock. Each mineral or rock has a characteristic optimal temperature and duration for complete nitrogen release. Preheating, under-heating or over-heating can cause nitrogen loss and isotopic shift. Therefore, we recommend using the offline combustion techniques and the optimal combustion conditions obtained in this study for nitrogen quantification and isotopic analysis of silicate minerals and rocks.

Mid-infrared observations of the nucleus of Comet P/2016 BA14 (PANSTARRS)

We present mid-infrared observations of comet P/2016 BA14 (PANSTARRS), which were obtained on UT 2016 March 21.3 at heliocentric and geocentric distances of 1.012 au and 0.026 au, respectively, approximately 30 h before its closest approach to Earth (0.024 au) on UT 2016 March 22.6. Low-resolution (λ/Δλ ~ 250) spectroscopic observations in the N-band and imaging observations with four narrow-band filters (centered at 8.8, 12.4, 17.7 and 18.8 μm) in the N- and Q-bands were obtained using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on the 8.2-m Subaru telescope atop Maunakea, Hawaii. The observed spatial profiles of P/2016 BA14 at different wavelengths are consistent with a point-spread function. Owing to the close approach of the comet to the Earth, the observed thermal emission from the comet is dominated by the thermal emission from its nucleus rather than its dust coma. The observed spectral energy distribution of the nucleus at mid-infrared wavelengths is consistent with a Planck function at temperature T ~ 350 K, with the effective diameter of P/2016 BA14 estimated as ~0.8 km (by assuming an emissivity of 0.97). The normalized emissivity spectrum of the comet exhibits absorption-like features that are not reproduced by the anhydrous minerals typically found in cometary dust coma, such as olivine and pyroxene. Instead, the spectral features suggest the presence of large grains of phyllosilicate minerals and organic materials. Thus, our observations indicate that an inactive small body covered with these processed materials is a possible end state of comets.

Quantifying the contribution of phyllosilicate mineralogy to aggregate stability in the East Asian monsoon region

Aggregate stability strongly influences soil function and has been a key indicator of soil quality and susceptibility to erosion. Although clay mineralogy has been recognized to have substantial effects on aggregate stability, little quantitative information is available on the specific contribution of various phyllosilicates in clay fraction. This study aimed to quantify the individual and combined effects of phyllosilicate minerals and their interaction with other soil properties on aggregate stability and breakdown mechanisms. A wide range of soil types in heavy textures from quaternary sediments were sampled under three land uses (forest, grass and arable) and at different genetic horizons along the mid-temperate to tropical climate gradient in the East Asian monsoon region. Soil aggregate stability against slaking (MWDFW), mechanical breakdown (MWDWS) and differential swelling (MWDSW) was determined, as well as phyllosilicate mineralogy by X-ray diffraction and a series of soil properties related to porosity, texture, organic matter, sesquioxides, and exchangeable cations. Aggregate stability generally exhibited a unimodal geographic trend (MWDSW in 1.85 ~ 3.49 mm, MWDWS in 0.76 ~ 3.22 mm and MWDFW in 0.14 ~ 2.74 mm), which became more remarkable with increased disruptive forces (coefficient of variation in 9 ~ 59%). Correspondingly, the dominant mechanisms of aggregate breakdown shifted from both slaking and mechanical breakdown to only slaking with increased soil weathering. The profile variation of aggregate stability and the land use effect differed with soil type and disruptive force. For phyllosilicate mineralogy, vermiculite had the largest explanatory power in aggregate stability (R2 = 54%, p < 0.001), followed by kaolilite and 1.4 nm intergrade mineral (R2 = 28 ~ 32%, p < 0.01), while illite explained little variance (R2 = 6%, p > 0.05), demonstrating the more prominent role of phyllosilicate mineralogy than other soil properties (R2 < 43%) in aggregate stabilization. Besides the dominant effect of vermiculite, soil organic carbon, exchangeable sodium and calcium exerted a complimentary effect (R2 = 12%). Collectively, aggregate stability is predominantly influenced by phyllosilicate mineralogy (especially swelling minerals) at the regional scale and by soil organic matter and exchangeable cations at the soil pedon scale.

Tracking Acid Generating Minerals and Trace Metal Spread from Mines using Hyperspectral Data: Case Studies from Northwest India

ABSTRACT A flight campaign over sites in India using the National Aeronautics and Space Administration (NASA) Airborne Visible Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) was undertaken in 2016. Among the sites overflown were abandoned and active mining sites, Ambaji and Zawar, in northwestern India in the states of Gujarat and Rajasthan. AVIRIS-NG data was examined for signs of acid-generating minerals that could contribute to acid mine drainage and for distinct minerals or changes in spectral absorption features that could be signs of contamination by trace metals released by mining activities. Processing approaches used included an expert system/spectral feature fitting programme, MICA (Material Identification and Classification Algorithm), that matches absorption features in image spectra to those in user-defined library spectra. Also used were low abundance material detection approaches. Over the Ambaji site, the acid-generating mineral jarosite was mapped with the MICA approach and relative abundance was mapped with a low probability detection algorithm. The Zawar mine has a better-defined drainage which was mapped with MICA. A larger number of phyllosilicate minerals were mapped in the Tiri River drainage from the Zawar mine than were observed in similar sized rivers in other Ambaji and Zawar AVIRIS-NG flightlines. The 2.2 μm absorption feature associated with the minerals mapped in these drainages was examined to determine band parameters associated with the absorption. It was determined that minerals mapped, including montmorillonite, muscovite, and illite had a wider scatter in band parameters, principally asymmetry, but to a lesser extent bandwidth, than similar exposures of these mineral classes in the other riverbeds in the AVIRIS-NG scenes. Also mapped in the Tiri River, using a spectral matched filter, were gypsum precipitates. Field samples of this precipitate had high trace metal abundances. The combination of mapping the precipitates, such as gypsum, and an association with distorted absorption features (due to trace metal adsorption) holds the prospect for using imaging spectrometer data to assess the spread of trace metals from mining sites.

Depression Mechanism of a Novel Depressant on Serpentine Surfaces and Its Application to the Selective Separation of Chalcopyrite from Serpentine

ABSTRACT Serpentine, a typically magnesium phyllosilicate gangue mineral, is often associated with chalcopyrite. In the process of flotation, serpentine is easy to get into the concentrate together with useful minerals, which seriously affects the quality of concentrate products. In this study, galactomannan (GM) was introduced for effectively separating chalcopyrite from serpentine with sodium butyl xanthate used as the collector. Its depression performance and adsorption mechanism were investigated through micro-flotation tests, zeta potential, FTIR, and XPS measurements. Micro-flotation test results showed that GM depressed serpentine more stronger than that of the chalcopyrite at a wide pH range of 3–8. An excellent separation of chalcopyrite and serpentine was achieved using GM as the depressant with a lower dosage of 40 mg/L, for which the flotation recovery of chalcopyrite was more than 80% and that of serpentine was close to 0. Zeta potential, FTIR, and XPS results illustrated that GM was chemically adsorbed on the serpentine surface through the interaction of the hydroxyl groups of GM with the Mg atoms on the serpentine surface. The formation of Mg(OH)2 enhanced the hydrophilicity of serpentine and inhibited the adsorption of flotation reagents onto the serpentine surface, and thereby decreasing its floatability. Therefore, GM could be used as a potential depressant of serpentine owing to its high selectivity, low dosage, environment protection, and low cost.

Identification of Phyllosilicates in the Antarctic Environment Using ASTER Satellite Data: Case Study from the Mesa Range, Campbell and Priestley Glaciers, Northern Victoria Land

In Antarctica, spectral mapping of altered minerals is very challenging due to the remoteness and inaccessibility of poorly exposed outcrops. This investigation evaluates the capability of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite remote sensing imagery for mapping and discrimination of phyllosilicate mineral groups in the Antarctic environment of northern Victoria Land. The Mixture-Tuned Matched-Filtering (MTMF) and Constrained Energy Minimization (CEM) algorithms were used to detect the sub-pixel abundance of Al-rich, Fe3+-rich, Fe2+-rich and Mg-rich phyllosilicates using the visible and near-infrared (VNIR), short-wave infrared (SWIR) and thermal-infrared (TIR) bands of ASTER. Results indicate that Al-rich phyllosilicates are strongly detected in the exposed outcrops of the Granite Harbour granitoids, Wilson Metamorphic Complex and the Beacon Supergroup. The presence of the smectite mineral group derived from the Jurassic basaltic rocks (Ferrar Dolerite and Kirkpatrick Basalts) by weathering and decomposition processes implicates Fe3+-rich and Fe2+-rich phyllosilicates. Biotite (Fe2+-rich phyllosilicate) is detected associated with the Granite Harbour granitoids, Wilson Metamorphic Complex and Melbourne Volcanics. Mg-rich phyllosilicates are mostly mapped in the scree, glacial drift, moraine and crevasse fields derived from weathering and decomposition of the Kirkpatrick Basalt and Ferrar Dolerite. Chlorite (Mg-rich phyllosilicate) was generally mapped in the exposures of Granite Harbour granodiorite and granite and partially identified in the Ferrar Dolerite, the Kirkpatrick Basalt, the Priestley Formation and Priestley Schist and the scree, glacial drift and moraine. Statistical results indicate that Al-rich phyllosilicates class pixels are strongly discriminated, while the pixels attributed to Fe3+-rich class, Fe2+-rich and Mg-rich phyllosilicates classes contain some spectral mixing due to their subtle spectral differences in the VNIR+SWIR bands of ASTER. Results derived from TIR bands of ASTER show that a high level of confusion is associated with mafic phyllosilicates pixels (Fe3+-rich, Fe2+-rich and Mg-rich classes), whereas felsic phyllosilicates (Al-rich class) pixels are well mapped. Ground truth with detailed geological data, petrographic study and X-ray diffraction (XRD) analysis verified the remote sensing results. Consequently, ASTER image-map of phyllosilicate minerals is generated for the Mesa Range, Campbell and Priestley Glaciers, northern Victoria Land of Antarctica.

Spectral characterization of the craters of Ryugu as observed by the NIRS3 instrument on-board Hayabusa2

C-type rubble pile asteroid (162173) Ryugu was observed and characterized up close for a year and a half by the instruments on-board the Japanese Aerospace eXploration Agency (JAXA) Hayabusa2 spacecraft. The asteroid exhibits relatively homogeneous spectral characteristics at near-infrared wavelengths (~1.8–3.2 μm), including a very low reflectance factor, a slight positive (“red”) slope towards longer wavelengths, and a narrow absorption feature centered at 2.72 μm that is attributed to the presence of OH− in phyllosilicate minerals. Numerous craters have been identified at the surface that provide good candidates for identifying and studying younger and/or more recently exposed near-surface material to further assess potential spectral/compositional heterogeneities. We present here the results of a spectral survey of all previously identified and referenced craters (Hirata et al. 2020) based on reflectance data acquired by the NIRS3 spectrometer, with an emphasis on the spectral characteristics between different craters as well as with their surrounding terrain. At a global scale, the spectral properties inside and outside of craters are found to be very similar, indicating that subsurface material is either compositionally similar to material at the surface that has a longer exposure age or that material at Ryugu's optical surface is spectrally altered over relatively short timescales by external factors such as space weathering. Although, the imaging data from ONC camera suites show more morphological and color diversity in craters at a smaller scale than the resolution provided by the NIRS3 instrument, which could indicate a wider compositional diversity on Ryugu than that observed in the near-infrared and discussed in this paper. The 2.72 μm band depth exhibit a slight anti-correlation with the reflectance factor selected at 2 μm, which could indicate different surface properties (e.g., grain size and/or porosity) or different alteration processes (e.g., space weathering, shock metamorphism and/or solar heating). Four different spectral classes were identified based on their reflectance factor at 2 μm and 2.72 μm absorption strength. The most commonly spectral behavior associated with crater floors, is defined by a slightly lower reflectance at 2 μm and deeper band depth. These spectral characteristics are similar to those of subsurface material excavated by the Hayabusa2 small carry-on impactor (SCI) experiment, suggesting these spectral characteristics may represent materials with a younger surface exposure age. Alternatively, these materials may have experienced significant solar heating and desiccation to form finer grains that subsequently migrated towards and preferentially accumulated in areas of low geopotential, such as craters floors. It is believed that the Hayabusa2 mission successfully collected typical surface material as well as darker material excavated by the SCI experiment, and detailed analyses of those samples upon their return will allow for further testing of these formation and alteration hypotheses.

Volatile-rich Asteroids in the Inner Solar System

Abstract Bennu (101195), target of the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) mission, is a type-B asteroid with abundant spectral evidence for hydrated silicates, low thermal inertia “boulders” and frequent bursts of particle emission. We suggest that Bennu’s parent body formed in the outer solar system before it was perturbed into the asteroid belt and then evolved into a near-Earth object. We show that this is consistent with models of planetesimal evolution. Bennu has many characteristics expected for a dormant comet, and could potentially contain a minimum of 1 wt.% adsorbed water if its gross mineralogy is consistent with the Orgueil meteorite. This is in addition to any ice or water contained within the hydrous minerals themselves. Based on this hypothesis, we predict the properties of the samples that will be returned to Earth by the OSIRIS-REx mission, including abundant phyllosilicate minerals, amorphous hydrated silicates and low-density, very high-porosity aggregates, already observed by the OSIRIS-REx instrument suite. We predict enrichments in D/H and 15N/14N, high C/Mg ratios (&gt;∼7 wt%), and a greater range of organic compositions than found in meteorites, including an organic component poor in aromatics, and a more labile organic fraction. Ammonium salts, ranging from NH4Cl to ammonium–organic acid salts could carry much of the nitrogen in comets, yet only NH4CH3COO and heavier salts are sufficiently stable to be found in these returned samples. Water adsorbed onto highly porous grains should also be detected provided that the sample return capsule remains below 300 K during Earth return, and this water should be isotopically heavy.

Laboratory geomechanical and petrophysical characterization of Longmaxi shale properties in Lower Silurian Formation, China

The Lower Silurian Longmaxi formation is one of the most promising shale gas reservoirs in China. A comprehensive understanding of the shale geomechanical and petrophysical properties is crucial for the successful exploration and extraction of shale gas. We select four representative locations to acquire Longmaxi formation shale samples for the laboratory experiments, to investigate the geomechanical and petrophysical properties through a series of X-ray diffraction (XRD), scanning electron microscope (SEM), uniaxial compression, triaxial compression, tensile strength, and fracture toughness measurements. Laboratory results indicate that: (1) The quartz is the dominant mineral, and phyllosilicate mineral contents vary largelly from 7.30% to 47.80% in Longmaxi shale, which enables a higher brittleness index and fracbility. SEM results show that the high gas storage potential and well micro-fractures development of Longmaxi shale rocks. (2) The phyllosilicate content is vital in determining the uniaxial compressive strength, triaxial strength and elastic properties due to its weaker mechanical properties than tectosilicate minerals; (3) Fracture toughness of Longmaxi shale are relatively higher than shale formations in the USA, which indicate a higher potential to form fracture networks during hydraulic fracturing operations. (4) The anisotropy affects Longmaxi shale mechanical properities extensively due to the high-density bedding planes, which may further influence the fracture network formation during hydraulic fracturing operations. Our results revealed significant non-linear mechanical response as a consequence of shale fabric and mineralogy, which provides necessary information for the in-situ hydraulic fracturing and wellbore stability application during shale gas development in Longmaxi shale formation.

Synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by talc and other phyllosilicates

Naturally occurring phyllosilicate minerals such as talc and vermiculite in conjunction with n-tetra butyl ammonium bromide (TBAB) co-catalyst were found to be efficient in the coupling of CO2 with epoxides to form cyclic carbonates. The reaction was carried out in a pressurized autoclave reactor at moderate pressures of 10–35 bars and temperatures of 100–150 °C. The optimized catalyst system exhibited > 90% conversion of the epoxides and > 90% selectivity for the desired cyclic carbonates, in the presence or absence of a solvent. The selectivity of the catalytic system could be improved with heat pre-treatment of the phyllosilicates albeit this resulted in slightly lower epoxide conversion. The results obtained using the heat treated phyllosilicates strongly support the hydrogen bond assisted mechanism for the cycloaddition of epoxides and CO2. The cycloaddition reaction could also be carried out in the absence of TBAB, although lower cyclic carbonate yields were observed. The phyllosilicate part of the catalyst system is heterogeneous, easy to separate after completion of reactions and reusable a number of runs without loss of activity.