Total Phyllosilicate Research Articles

Quantitative clay mineralogy predicts radiocesium bioavailability to ryegrass grown on reconstituted soils

Current radiocesium (137Cs) models to evaluate the risk of 137Cs transfer from soil to plants are based on the clay and exchangeable potassium (K) contents in soil. These models disregard the mineralogy of the clay fraction and are likely not capable of accurately predicting the 137Cs transfer factor (TF) in soils of contrasting parent rocks and weathering stages. The objectives of this study were to test that hypothesis and to identify whether quantitative information on mineralogy can improve the predictions. A pot cultivation experiment was set up with clay-sand mixtures in single and double clay doses that were fertilized, spiked with 137Cs and grown with ryegrass for 30 days. Four clays (illite, biotite, smectite and vermiculite) along with six deposits from clay-rich geological units were compared. The TF generally decreased with increasing clay dose for each of these ten different clay groups, however, the TF varied two orders of magnitude across clay groups and doses. The TF was highest for clays with little 137Cs specific sites such as bentonite and/or where the exchangeable K content was low compared to the other clays. The TF was well predicted from the soil solution 137Cs and K concentrations (R2 = 0.72 for log transformed TF), corroborating earlier findings in natural soils. The TF (log transformed) was statistically unrelated to total phyllosilicate content or 1:1 and 2:1:1 type phyllosilicate content while it significantly decreased with increasing 2:1 phyllosilicate content (R2 = 0.32). A multiple regression model with four different X-ray diffraction (XRD) based phyllosilicate groups yielded the strongest predictive power (R2 = 0.74). We conclude that XRD quantification is valuable for describing 137Cs bioavailability in plant substrates. These findings now await confirmation for natural soils.

Mapping Phyllosilicates on the Asteroid Bennu Using Thermal Emission Spectra and Machine Learning Model Applications

AbstractBennu, the target of the OSIRIS‐REx mission, is an asteroid with compositions analogous to low petrologic type CI, CM, CR, and/or ungrouped carbonaceous chondrites. Asteroids like Bennu provide information about the building blocks of the early Solar System. Analysis of the mid‐infrared remote sensing data informs mineral quantification. We apply a phyllosilicate specific model, developed by Breitenfeld et al. (2021, https://doi.org/10.1029/2021je007035) that distinguishes between Mg and Fe serpentines, to Baseball Diamond 1 (BBD1), equatorial station 3 (EQ3), and touch‐and‐go OSIRIS‐REx thermal emission spectrometer data. The average total phyllosilicate predictions are 73 (BBD1) and 72 vol% (EQ3). We observe higher Fe‐cronstedtite and lower Mg‐rich serpentine content in the equatorial region of Bennu than average. Mid‐infrared spectral variability may be explained by sorting effects through mass movement.

Linking mineralogy and spectroscopy of highly aqueously alteredCMandCIcarbonaceous chondrites in preparation for primitive asteroid sample return

AbstractThe highly hydrated, petrologic type 1CMandCIcarbonaceous chondrites likely derived from primitive, water‐rich asteroids, two of which are the targets forJAXA's Hayabusa2 andNASA'sOSIRIS‐REx missions. We have collected visible and near‐infrared (VNIR) and mid infrared (MIR) reflectance spectra from well‐characterizedCM1/2,CM1, andCI1 chondrites and identified trends related to their mineralogy and degree of secondary processing. The spectral slope between 0.65 and 1.05 μm decreases with increasing total phyllosilicate abundance and increasing magnetite abundance, both of which are associated with more extensive aqueous alteration. Furthermore, features at ~3 μm shift from centers near 2.80 μm in the intermediately alteredCM1/2 chondrites to near 2.73 μm in the highly alteredCM1 chondrites. The Christiansen features (CF) and the transparency features shift to shorter wavelengths as the phyllosilicate composition of the meteorites becomes more Mg‐rich, which occurs as aqueous alteration proceeds. Spectra also show a feature near 6 μm, which is related to the presence of phyllosilicates, but is not a reliable parameter for estimating the degree of aqueous alteration. The observed trends can be used to estimate the surface mineralogy and the degree of aqueous alteration in remote observations of asteroids. For example, (1) Ceres has a sharp feature near 2.72 μm, which is similar in both position and shape to the same feature in the spectra of the highly alteredCM1MIL05137, suggesting abundant Mg‐rich phyllosilicates on the surface. Notably, bothOSIRIS‐REx and Hayabusa2 have onboard instruments which cover theVNIRandMIRwavelength ranges, so the results presented here will help in corroborating initial results from Bennu and Ryugu.

Classification of hydrous meteorites (CR, CM and C2 ungrouped) by phyllosilicate fraction: PSD-XRD modal mineralogy and planetesimal environments

The relative differences in the degree of hydration should be reflected in any classification scheme for aqueously altered meteorites. Here we report the bulk mineralogies and degree of hydration in 37 different carbonaceous chondrites: Renazzo-like (CR), Mighei-like (CM), and ungrouped (type 2) samples. This is achieved by quantifying the modal abundances of all major (phases present in abundances >1wt.%) minerals using Position Sensitive Detector X-ray Diffraction (PSD-XRD). From these modal abundances, a classification scheme is constructed that is based on the normalized fraction of phyllosilicate (total phyllosilicate/total anhydrous silicate+total phyllosilicate). Samples are linearly ranked from type 3.0 – corresponding to a phyllosilicate fraction of <0.05, to type 1.0 – corresponding to a total phyllosilicate fraction of >0.95. Powdered meteorite samples from any hydrated carbonaceous chondrite group can be ranked on this single classification scale. The resulting classifications for CRs exhibit a range from type 2.8 to 1.3, while for CMs the range is 1.7–1.2. The primary manifestation of aqueous alteration is the production of phyllosilicate, which ceased when the fluid supply was exhausted, leading to the preservation of anhydrous silicates in all samples. The variability in hydration indicates that either accretion of ices was heterogeneous or fluid was mobilized. From the bulk mineral abundances of the most hydrated samples, we infer that the initial mass fraction of H2O inside of their parent body(ies) asteroids was <20wt.%. Bulk carbonaceous chondrite mineralogy evolved towards increasingly oxidizing assemblages as the extent of bulk hydration increased. This is consistent with the escape of reducing H2 gas that is predicted to have been produced from water during hydration reactions.

Aqueous alteration on asteroids: Linking the mineralogy and spectroscopy of CM and CI chondrites

CM/CI meteorites range in degree of aqueous alteration suggesting differences in initially accreted materials including water ice and possible spatial heterogeneities within their parent bodies. As alteration progresses, the total abundance and magnesium content of phyllosilicates increases. In this paper we present the results of a coordinated spectral–mineralogical study of a well-characterized suite of CM/CI meteorites that range from 60 to 90% alteration. By acquiring spectra the same meteorite powders as Howard et al. (Howard, K.T., Benedix, G.K., Bland, P.A., Cressey, G. [2009]. Geochim. Cosmochim. Acta 73, 4576–4589; Howard, K.T., Benedix, G.K., Bland, P.A., Cressey, G. [2011]. Geochim. Cosmochim. Acta 75, 2735–2751) and Bland et al. (Bland, P.A., Cressey, G., Menzies, O.N. [2004]. Meteorit. Planet. Sci. 39(1), 3–16), we are able for the first time to directly correlate mineralogy with features in reflectance spectra. At visible/near-infrared wavelength, the presence of a 0.7-μm charge transfer band is indicative of aqueous alteration. However, not all altered CM/CI meteorites exhibit this feature; thus the lack of a 0.7μm absorption band in asteroids does not necessarily signify a lack of aqueous alteration. Furthermore, the position and depth of 0.7-μm charge transfer band shows no correlation with the mineralogical changes associated with aqueous alteration. Similarly, the near-infrared slope, which is not directly related to the mineralogic progression associated with increasing alteration, is not unambiguously related to degree of alteration in the CM/CI meteorites studied. However, the mid-infrared reflectance spectra of CM/CI meteorites contain a broad absorption feature in the 10–13-μm region, which is a convolution of vibrational features due to Mg-rich phyllosilicates and unaltered olivine. The overall feature continuously changes with total phyllosilicate abundance from a shorter wavenumber/longer wavelength peak (815cm−1, 12.3-μm) for less altered meteorites to a longer wavenumber/shorter wavelength (875cm−1, 11.4-μm) peak in the highly altered meteorites, with roughly equal spectral contributions producing a doublet in intermediately altered meteorites, Using the results from the mid-infrared analyses of meteorite spectra, it is possible to estimate the degree of alteration on dark primitive asteroids. We find Asteroid (24) Themis to have a 1000–700cm−1 (10–13-μm) peak at longer wavelengths suggesting Themis has a complex surface mineralogy with approximately 70vol.% phyllosilicates and 25vol.% anhydrous silicates.

Long-range transport of giant particles in Asian dust identified by physical, mineralogical, and meteorological analysis

Abstract. Giant particles transported over long distances are generally of limited concern in atmospheric studies due to their low number concentrations in mineral dust and possible local origin. However, they can play an important role in regional circulation of earth materials due to their enormous volume concentration. Asian dust laden with giant particles was observed in Korea on 31 March 2012, after a migration of about 2000 km across the Yellow Sea from the Gobi Desert. Scanning electron microscopy (SEM) revealed that 20% of the particles exceeded 10 μm in equivalent sphere diameter, with a maximum of 60 μm. The median diameter from the number distribution was 5.7 μm, which was larger than the diameters recorded of 2.5 and 2.9 μm in Asian dust storms in 2010 and 2011, respectively, and was consistent with independent optical particle counter data. Giant particles (&gt;10 μm) contributed about 89% of the volume of the dust in the 2012 storm. Illite–smectite series clay minerals were the major mineral group followed by quartz, plagioclase, K-feldspar, and calcite. The total phyllosilicate content was ~52%. The direct long-range transport of giant particles was confirmed by calcite nanofibers closely associated with clays in a submicron scale identified by high-resolution SEM and transmission electron microscopy. Since giant particles consisted of clay agglomerates and clay-coated quartz, feldspars, and micas, the mineral composition varied little throughout the fine (&lt;5 μm), coarse (5–10 μm), giant-S (10–20 μm), and giant-L (&gt;20 μm) size bins. Analysis of the synoptic conditions of the 2012 dust event and its migration indicated that the mid-tropospheric strong wind belt directly stretching to Korea induced rapid transport of the dust, delivering giant particles. Giant dust particles with high settling velocity would be the major input into the terrestrial and marine sedimentary and ecological systems of East Asia and the western Pacific. Analysis of ancient aeolian deposits in Korea suggested the common deposition of giant particles from Asian dust through the late Quaternary Period. The roles of giant particles should be reviewed with regard to regional circulation of mineral particles and nutrients.

Modal mineralogy of CM chondrites by X-ray diffraction (PSD-XRD): Part 2. Degree, nature and settings of aqueous alteration

Within 5 million years after formation of calcium aluminium rich inclusions (CAI), high temperature anhydrous phases were transformed to hydrous phyllosilicates, mostly serpentines, which dominate the matrices of the most primitive carbonaceous chondrites. CMs are the largest group of meteorites to provide samples of this material. To understand the nature of the availability, and role of H 2O in the early solar system – as well as the settings of aqueous alteration – defining CM petrogenesis is critical. By Position Sensitive Detector X-ray Diffraction (PSD-XRD), we determine the modal abundance of crystalline phases present in volumes >1% for a suite of CMs – extending Part 1 of this work that dealt only with CM2 falls ( Howard et al., 2009) to now include CM2 and CM1 finds. CM2 samples contain 13–31% Fe,Mg silicates (olivine + pyroxene) and from 67% to 82% total phyllosilicate (mean 75% ± 1.3 2 σ). CM1 samples contain 6–10% olivine + pyroxene and 86–88% total phyllosilicate. Magnetite (0.6–5.2%), sulphide (0.6–3.9%), calcite (0–1.9%) and gypsum (0–0.8%) are minor phases across all samples. Since phyllosilicate forms from hydration of anhydrous Fe,Mg silicates (olivine + pyroxene), the ratio of total phyllosilicate to total anhydrous Fe,Mg silicate defines the degree of hydration and the following sequence results (in order of increasing hydration): QUE 97990 < Y 791198 < Murchison < Murray < Mighei < ALHA 81002 < Nogoya ⩽ Cold Bokkeveld ⩽ Essebi < QUE 93005 < ALH 83100 < MET 01070 < SCO 06043. High activities of Al (mostly from reactive mesostasis) and Si help to explain the composition and structure of CM serpentines that are distinct from terrestrial standards. Our data allows inference as to CM mineralogy at the point of accretion and challenges the conceptual validity of progressive alteration sequences. Modal mineralogy also provides new insights into CM petrogenesis and hints at a component of aqueous alteration occurring in the nebula, in addition to on the CM parent body(ies).

Changes in mineralogy of loess–paleosol sections across the Chinese Loess Plateau

Quantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the Chinese Loess Plateau (CLP). Mineralogy, geochemistry, and single-particle petrography of loess and paleosols are relatively uniform over the CLP. However, in detail, there are mineralogical changes related to eolian process and chemical weathering. Particle-size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals. After deposition, detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite, dolomite, biotite, illite, chlorite, amphibole, and plagioclase. The weathering of biotite, chlorite, and illite resulted in a significant increase of expandable phyllosilicate contents. The sequential weathering of the minerals is reflected chemically in the decrease of Na and Mg and the increase of iron oxidation. Mineralogy of the Chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient, and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the CLP.

Modal mineralogy of CM2 chondrites by X-ray diffraction (PSD-XRD). Part 1: Total phyllosilicate abundance and the degree of aqueous alteration

CM carbonaceous chondrites are samples of incompletely serpentinized primitive asteroids. Using position sensitive detector X-ray diffraction (PSD-XRD) and a pattern stripping technique, we quantify the modal mineralogy of CM2 chondrites: Mighei; Murray; Murchison; Nogoya and Cold Bokkeveld. There is a narrow range in the combined modal volume (vol%) of the most abundant phases Mg-serpentine (25–33%) and Fe-cronstedtite (43–50%). Cold Bokkeveld is anomalous in containing more Mg-serpentine (49–59%) than Fe-cronstedtite (19–27%). Even including Cold Bokkeveld, the range in modal total phyllosilicate is 73–79% (average = 75%). Total phyllosilicate abundance provides a non-ambiguous measure of the degree of aqueous alteration and indicates that these meteorites have all experienced essentially the same degree of aqueous alteration. This reflects pervasive hydration of matrix across CM2 samples. Apparent differences in the alteration of chondrules observed in petrographic studies represent various stages in the progression towards complete hydration of all components but are not manifest in significant differences in modal mineralogy. For all samples there is a limited range in olivine (6.9%) and pyroxene (5%) abundances. Modal abundances of the remaining identified phases also show a limited range: calcite (0–1.3%); gypsum (0–1.6%); magnetite (1.1–2.4%); pentlandite (0–2.1%) and pyrrhotite (1–3.8%). As expected, we observe a strong negative correlation in the modal abundance of anhydrous Fe–Mg silicates (olivine + pyroxene) and total phyllosilicate (Mg-serpentine + Fe-cronstedtite) consistent with the idea that phyllosilicate is forming by aqueous alteration of the anhydrous components. The negative correlation in the modal abundance between Mg–serpentine and Fe-cronstedtite indicates: (a) mineralogic transformation of Fe-cronstedtite to Mg-serpentine by fluid driven recrystallisation or (b) that these meteorites had different initial abundances of olivine and pyroxene. The observed positive correlation in the relative proportion of Mg-serpentine with increasing total phyllosilicate abundance reflects the evolution of increasingly Mg-rich phyllosilicate during aqueous alteration. Fe-cronstedtite is the dominant phyllosilicate, while CM chondrule olivines are forsteritic and will form Mg-serpentine during aqueous alteration. This implies that matrix olivine was more Fe-rich than chondrule olivine prior to aqueous alteration.

Clay fabric intensity in natural and artificial fault gouges: Implications for brittle fault zone processes and sedimentary basin clay fabric evolution

The role of phyllosilicate fabrics in fault gouge is a poorly understood component of the mechanical and hydrologic behavior of brittle fault zones. We present 90 fabric intensity measurements using X‐ray texture goniometry on 22 natural clay‐rich fault gouges from low‐angle detachment faults (Death Valley area detachments, California; Ruby Mountains, Nevada; West Salton Detachment Fault, California) and the Peramola thrust in NE Spain. Natural fault gouges have uniformly weak clay fabrics (multiples of a random distribution (MRD) = 1.7–4.5, average MRD = 2.6) when compared to phyllosilicate‐rich rocks found in other geologic settings. Clay fabric intensities in natural gouges do not vary significantly either as a function of tectonic environment or of dominant clay mineralogy in the gouge. We compare these natural samples with 69 phyllosilicate fabric intensities measured in laboratory experiments on synthetic clay‐quartz mixtures. Clay fabric intensities from laboratory samples are similar to those in natural gouges (MRD = 1.7–4.6), but increase systematically with increasing shear strain and normal stress. Total phyllosilicate content does not significantly affect clay fabric intensity. Shear strain is important for developing stronger fabrics; samples subjected solely to compression exhibit uniformly weak fabrics (MRD = 1.6–1.8) even when compressed at high normal stresses (150 MPa). The weak fabrics found in natural fault gouge indicate that if anisotropic and overall low fault zone permeability allow elevated pore fluid pressures and fault weakening, this anisotropy must be a transient feature that is not preserved. Our data also reinforce the idea that clay fabric development in sedimentary rocks is primarily a function of authigenic mineral growth and not of compaction‐induced particle rotation.

Quantitative bulk and single-particle mineralogy of a thick Chinese loess–paleosol section: implications for loess provenance and weathering

A 40 m loess–paleosol section (L1, S1, and upper L2) at the semi-arid western margin of the Chinese Loess Plateau was investigated by quantitative mineralogical, microscopic, and geochemical analyses of bulk samples and single particles. The average ( N=16) mineralogical composition of loess in the studied section is 34.8% quartz, 15.3% plagioclase, 5.0% K-feldspar, 25.1% phyllosilicates, 11.7% calcite, 3.3% dolomite, and 1.9% amphibole. Ratios of plagioclase, K-feldspar, and amphibole to quartz do not change throughout both the loess and paleosol units, while the ratio of total phyllosilicate to quartz is enhanced in the paleosol where there is significant variation in calcite and dolomite contents. Illite and interstratified illite–smectite are the most abundant (84±4%) clay minerals in the clay fraction of both loess and paleosol samples. The calcite/dolomite ratio, Mg/Si ratio, iron oxidation degree, and organic carbon contents are positively correlated to magnetic susceptibility. Weathering and elemental mobilization in paleosol samples was indicated by calcite–dolomite dissolution, nanofiber–calcite reprecipitation, and biotite–hydrobiotite transformation, while there was no notable evidence for weathering observed in loess samples. The essentially pristine state of loess samples with respect to weathering and the minimal alteration of minerals in the paleosol indicate relatively poor weathering conditions at both the depositional and source sites. Analysis of single particles show that most plagioclase is albitic, calcite occurs frequently in particles with dolomite but also with silicates, biotite is associated with barite–celestine inclusions, iron oxide occurs as a pseudomorph after framboidal pyrite, and rock fragments may be siliciclastic sedimentary, metasedimentary, and granitic. These observations indicate that the lithology of source regions must have been dominated by largely siliciclastic and carbonate sedimentary rocks and their low-grade metamorphic equivalents with contributions from granitoids partly affected by hydrothermal alterations and possibly high-grade metamorphic rocks. The mineralogical analysis of loess and paleosols opens new ground for refining the established climatic proxies, and for tracking source lithology and weathering in the source and depositional regions.

Bulk and single‐particle mineralogy of Asian dust and a comparison with its source soils

The mineralogical properties of Asian dust have been examined in detail, and the results have been compared with the Chinese source soils using high‐resolution scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, and chemical analysis. Mineralogical classification of Asian dust particles showed that the most common single particles were clay aggregates (48%) that were often mixed with nanosized calcite, followed by particles of quartz (22%), plagioclase (11%), coarse calcite (6%), K‐feldspar (5%), muscovite, chlorite, kaolinite, amphibole, gypsum, Fe and Ti oxides which were either partly or entirely attached with clay‐size mineral grains. The clay minerals in Asian dust were mostly illite and interstratified illite‐smectite. The average mineral composition of the bulk dust samples by X‐ray diffraction was quartz (28%), plagioclase (11%), K‐feldspar (8%), calcite (8%), illite (19%), interstratified illite‐smectite (22%), chlorite (2%), smectite (1%), and kaolinite (1%). In the silty soils from the source regions, the clay minerals and nanosized pedogenic calcite aggregated and covered silt‐size minerals, while the sands were mostly composed of quartz and feldspars and were lined with clay minerals. The mineralogy of Asian dust was similar to that of the silty soil from the loess plateau, but the total phyllosilicate content increased from desert sands (7%), silty soil (23%), to Asian dust (45%), fining eastward. The optical properties of Asian dust and its interaction with atmospheric gases and cloud are probably affected by the clay‐rich mineral composition, the aggregation and attachment of the clay minerals on the coarser minerals, and the nanosized calcite.