Orals: Wed, 30 Apr | Room 0.96/97
Garnet, being one of the most widespread minerals in the Earth, plays a crucial role for the investigation of many geological processes. Garnet occurs in several ultramafic to felsic rocks (e.g. mantle peridotites, granulites and metamorphic rocks) and as detrital mineral in sediments [1], and crystallize from the crust to the Transition Zone in the mantle thanks to its broad P-T stability field (P ⁓25 GPa and T ⁓2000 °C [2, 3]). These features, along with the chemical variability and the peculiar resistance, make garnet an essential tool to determine the P-T-t history and the evolution of rocks.
Garnet is commonly defined as the archetypal cubic mineral, since it typically presents Ia-3d space group and isotropic optical properties under cross polarized light [4]. Despite that, occurrences of birefringent garnets have been reported [5, 6, 7]. In most cases, these “uncommon” samples have specific chemical characteristics, such as hydrogrossular (Ca3Al2(SiO4)3-x(H4O4)x) and “grandite” (solid solution between grossular and andradite (Ca3(Al,Fe3+)2(SiO4)3)) compositions. In these specimens, the optical birefringence is explained as a consequence of symmetry reduction, from cubic to tetragonal or orthorhombic, possibly due to cation ordering in octahedral sites or to the presence of a significant hydrogarnet component [5, 6, 7].
Recent findings of sector-zoned birefringent and anhydrous garnets with almandine-grossular, (Fe2+,Ca)3Al2(SiO4)3, composition in blueschist- and greenschist-facies metamorphic rocks from several worldwide localities (e.g. Farinole, Cazadero, Jenner and eastern Italian Alps) suggested that optically anisotropic, probably not-cubic garnets could be more common than generally assumed [8]. Cesare et al. [8] proposed that these garnets could initially grow tetragonal in low-grade (T <450 °C) rocks, with possible implications about the use of this mineral as a marker for the processes occurring in such geological contexts. However, the causes of symmetry reduction (from cubic to tetragonal) and of the associated birefringence are not clear and a more detailed investigation is required.
Here, we report new crystallographic studies on sector-zoned and anhydrous garnets with almandine-grossular composition in low-grade metamorphic metabasites from Cazadero (USA) and metapelites from the SW Tauern Window (Italy). The investigation was carried out combining both single-crystal X-ray and electron diffraction techniques. In addition, electron energy-loss spectroscopy (EELS) has been performed to detect the presence and amounts of Fe3+ or Mn3+ in the studied garnets. Our results suggest that birefringence is caused by a symmetry reduction from cubic to orthorhombic system, as proposed by [7], connected with twinning and/or subsequent exsolution processes. The reduction of symmetry is due to the ordering of cations and is supported by the statistical analyses of diffracted intensities.
References:
[1] Baxter EF et al. (2013) Elements 9: 415-419
[2] Ringwood AE (1991) Geochim Cosmochim Acta 55: 2083-2110
[3] Wood BJ et al. (2013) Elements 9: 421-426
[4] Grew ES et al. (2013) Am Min 98: 785-810
[5] Allen FM and Buseck PR (1988) Am Min 73: 568-584
[6] Antao SM (2013) Powder Diffr 28(4): 281-288
[7] Xu H et al. (2023) Am Min 108: 572-583
[8] Cesare B et al. (2019) Sci Rep 9: 14672
How to cite: Lorenzon, S., Mugnaioli, E., Biagioni, C., Livi, K., Nestola, F., and Cesare, B.: Garnet, not always the archetypal cubic mineral: new crystallographic evidences from Cazadero (USA) and the SW Tauern Window (Italy) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15971, https://doi.org/10.5194/egusphere-egu25-15971, 2025.
SiO2 is a crucial oxide in Earth and other terrestrial planets such as super-Earth, making the study of its high-pressure structural phase transitions and physical properties vital. Due to the extremely high pressures required for the phase transitions of SiO2, significant uncertainty exist in the high-pressure phase boundaries from experiments and theoretical calculations. Given the similarities in high-pressure structures between SiO2 and the AF2 difluorides, the latter serve as excellent analogs for studying the high-pressure properties of SiO2. The phase transition of AF2 difluorides strongly depends on cationic radius, pressure, and temperature. In this study, we investigated the phase transitions of MgF2, CaF2, and BaF2 at high pressures and temperatures using Raman spectroscopy and X-ray diffraction in diamond anvil cells up to 50 GPa at 300-700 K. These difluorides, with cationic radii of 0.72-1.35 Å, reveal the influence of cationic radius on structure of difluorides under extreme conditions.
Our results show that elevating temperature increases the transition pressure from rutile to the CaCl2-type phase but has a negative influence on the transition pressure when MgF2 transforms from the HP-PdF2- to cotunnite-type phase. Meanwhile, the transition pressure from the CaCl2- to HP-PdF2-type phase for MgF2 is identified to be independent of temperature. For both CaF2 and BaF2, elevating temperature leads to a lower transition pressure from fluorite to the cotunnite-type phase but has little influence on the transition to Ni2In structure. Our results are important for exploring the physical properties and the transition sequence of AX2-type minerals. The information of these difluorides could also help to understand the structure of the Earth and other terrestrial planets.
How to cite: Zhang, X., Sun, N., and Mao, Z.: Phase transitions of AF2 difluorides MgF2, CaF2, and BaF2 at high pressures and temperatures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5058, https://doi.org/10.5194/egusphere-egu25-5058, 2025.
As an accessory mineral in marine evaporites, polyhalite, K2MgCa2(SO4)4·2H2O, coexists with halite (NaCl) in salt formations, which are a potential type of geological repositories for permanent storage of high-level nuclear wastes. However, because of the heat generated by radioactive decays in the wastes, polyhalite (as well as other co-existing hydrous minerals such as clay and gypsum) may dehydrate, and the released water will dissolve its neighboring salt, potentially affecting the repository integrity. Thus, studying the thermal behavior of polyhalite is important. In this study, a polyhalite sample containing a small amount of halite was collected from the Salado formation at the WIPP site in Carlsbad, New Mexico. In-situ high-temperature synchrotron X-ray diffraction was conducted from room temperature to 1066 K with the sample powders sealed in a silica-glass capillary. At about 506 K, polyhalite started to decompose into water vapor, anhydrite (CaSO4) and two langbeinite-type phases, K2CaxMg2-x(SO4)3, with different Ca/Mg ratios. XRD peaks of the minor halite disappeared, presumably due to its dissolution by water vapor. With further increasing temperature, the two langbeinite solid solution phases displayed complex variations in crystallinity, composition and their molar ratio and then were combined into the single-phase triple salt, K2CaMg(SO4)3, at ~919 K. Rietveld analyses of the XRD data allowed determination of structural parameters of polyhalite and its decomposed anhydrite and langbeinite phases as a function of temperature. From the results, the thermal expansion coefficients of these phases have been derived, and the structural mechanisms of their thermal behavior been discussed. In addition, to determine phase stability relations, standard enthalpies of formation of polyhalite from constituent oxides and elements were measured using high-temperature drop-solution calorimetry.
How to cite: Xu, H.: Crystal structure and phase stability of polyhalite at high temperatures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2607, https://doi.org/10.5194/egusphere-egu25-2607, 2025.
The study of nanorocks (crystallized inclusions of anatectic melts) has been delivering in the last 15 years many intriguing novel insights into crustal anatectic processes at depth. From a mineralogical standpoint, the systematic use of micro-Raman Spectroscopy (MRS) on nanorocks has revealed that the mineral phases crystallizing from the melt in the inclusions are distinctive, for example, the feldspar polymorphs (kokchetavite, kumdykolite, svyatoslavite and dmisteinbergite) and the SiO2 polymorphs cristobalite and tridymite (Wannhoff et al., 2022). In addition, MRS data collected on samples from numerous localities worldwide have revealed the presence in nanorocks of two novel crystalline phases, which are the primary focus of this study. Initially identified for their unique micro-Raman spectra, their crystal structures have been solved ab-initio and refined through three-dimensional electron diffraction (3DED) data, collected with a TEM.
The first novel phase is pfaffenbergite (Ferrero et al., 2024), KNa3(Al4Si12)O32, which has the composition of an unmixed binary K-Na feldspar, hence it can be regarded as a feldspar polymorph. Its micro-Raman spectrum is characterized by a very strong vibrational mode at 412 cm-1 (hence its informal name of “phase 412”, e.g. Borghini et al., 2024), two secondary peaks at 105 cm-1 and 832 cm-1 and two weaker peaks at 130 cm-1 and 470 cm-1. 3DED revealed that pfaffenbergite is a hexagonal mineral, crystallizing in space group P6/mcc. This mineral can be classified as a sheet silicate and it is isostructural with kokchetavite (KAlSi3O8) and wodegongjieite (KCa3(Al7Si9)O32). The latter is a mineral recently found as crystallization product of melt in inclusions within corundum from chromitites in the Luobusa ophiolite (Tibet, China; Mugnaioli et al., 2022), and subsequently with pfaffenbergite in garnet from the Saxony Granulite Complex.
The second novel mineral has not yet been approved by the IMA CNMNC and it is being called provisionally “phase 430” from its main micro-Raman vibrational mode. Three secondary peaks are present at 186 cm-1, 264 cm-1 and 292 cm-1, along with two weaker peaks at 485 cm-1 and 823 cm-1. Our results show that this phase has the ideal formula KK2Na3(Al6Si36)O84 and crystallizes in the P6/mcc space group. The arrangement of tetrahedral sites (Si,Al) in “phase 430” resembles that of frameworks in feldspathoids, but with a topology not yet reported as far as we know.
We interpret pfaffenbergite, wodegongjieite and “phase 430” as metastable phases crystallizing rapidly in a silicate melt enclosed in a small pore under non-equilibrium conditions. The increasing number of recent findings of metastable phases suggests that these minerals are more common than expected. It is even possible that they may represent rock-forming minerals in natural rocks which experienced rapid cooling/rapid crystallization, for instance lavas and ignimbrites, along with experimental products involving silicate melts.
References
Borghini et al. (2024) Eur J Mineral 36, 279–300
Ferrero S et al (2024) IMA 2023-105, in CNMNC Newsletter 78, Eur J Mineral 36
Mugnaioli E et al (2022) Min Mag 1–13
Wannhoff I et al (2022) Am Min 107, 2315–2319
How to cite: Ferrero, S., Lorenzon, S., Borriello, R., Borghini, A., Wirth, R., Schreiber, A., Fuchs, R., O'Brien, P. J., Grew, E., and Mugnaioli, E.: Pfaffenbergite & “phase 430”, new minerals crystallizing in nanorocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13776, https://doi.org/10.5194/egusphere-egu25-13776, 2025.
Concrete and its basic components are essential resources in modern society, with their usage steadily increasing over the years. Ensuring the production of high-quality concrete mixtures is critical to the long-term economic sustainability and infrastructure progress of any developed nation. Coarse rock aggregates make up most of the total volume in any concrete structure. Therefore, their suitability and performance must be ensured through proper evaluation and selection. One of the most significant concrete issues associated with the use of unsuitable aggregates is Internal Sulfate Attack (ISA). ISA can occur when sulfide-containing lithotypes, namely pyrrhotite, become reactive after the concrete has set. Through a series of complex chemical reactions, pyrrhotite releases sulfur compounds into the cement paste, where they react with the primary hydrated phases to form expansive by-products. These secondary expansive mineral phases cause internal swelling and cracking, leading to a significant reduction in the structural integrity of the concrete. Currently, a procedure that measures the total sulfur content (TS%) of aggregates is widely used and serves as an effective screening method to quickly identify and select aggregates with low to no sulfide content. However, this analysis only reports the TS% of the entire sample and does not account for the presence of non-reactive sulfide minerals, such as chalcopyrite, pentlandite, and most types of pyrite. The objective of this study is to improve this widely used analysis by developing a selective dissolution protocol that can attribute the TS% of an aggregate sample to its specific pyrrhotite content. This will allow the accurate quantification of sulfur associated with pyrrhotite, the most reactive sulfide mineral. The methodology includes a primary analysis to determine the initial TS% of the sample. This is followed by two selective dissolution cycles to separate the sulfide phases present. The first step uses an HCl solution designed to selectively dissolve the pyrrhotite content. In the second step, the remaining sample is dissolved in an aqua regia solution to digest the other sulfide phases. The solid residue from the first dissolution is analyzed for TS%, representing the sulfur fraction associated with the other sulfide phases in the sample that are non-reactive in the context of ISA. The difference between the TS% value of the solid residue from the first dissolution and the initial TS% corresponds to the sulfur specifically associated with pyrrhotite. The final solid residue of the second dissolution is also analyzed for TS%, which should be negligible and close to zero. Preliminary results from aggregate samples with medium to high sulfur content have shown promising findings. Samples with up to 2.7% TS% showed negligible amounts of pyrrhotite content after the first dissolution step, with very low TS%, averaging 0.3% after the second dissolution. Samples with an initial TS% of 0.6% yielded an average TS% of 0.03% after the second dissolution phase. These results indicate that the parameters established for the method (acid strength, dissolution temperature, sample amount) perform as expected for the range of sulfur values currently under evaluation in the industry.
How to cite: Titon, B., Duchesne, J., Fournier, B., and Rodrigues, A.: Development of a selective dissolution protocol for pyrrhotite quantification in sulfide-bearing concrete aggregates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13329, https://doi.org/10.5194/egusphere-egu25-13329, 2025.
The presence of pollutant dyes in water bodies poses a significant concern that adversely impacts both human health and environmental integrity. Numerous methodologies and materials exist for the extraction of these contaminants from aqueous solutions and their subsequent utilization. Adsorption processes utilizing zeolite minerals and various modified forms are frequently employed.
The unmodified forms of zeolite minerals are inadequate for dye removal from aqueous solutions; consequently, the properties of zeolite can be enhanced through the application of various surfactants. Nevertheless, the organic surfactants utilized in enhancing zeolite efficacy are also contaminants, and further research is being conducted to eliminate these pollutants from aqueous environments. Furthermore, only organic surfactants and a limited number of distinct active substances have been utilized to enhance the dye removal efficacy of zeolites. While zeolite minerals modified with inorganic active substances such as NaCl, Na2CO3 and Na2SO4 have been utilized in various applications, the dye removal efficacy of zeolites modified with these inorganic salts has not been previously investigated.
In this study, as an alternative to organic surfactants conventionally employed for the modification of zeolite minerals in dye removal applications, the efficacy of previously untested inorganic active substances on zeolites was examined to provide a more environmentally sustainable option. Modification processes were conducted utilizing NaCl, Na2CO3, and Na2SO4, while control modifications were performed using HDTMA, a widely employed substance, to evaluate the comparative efficacy of these active compounds. The efficacy of the unmodified and modified zeolites was evaluated using Reactive Black 5 and Methylene Blue dyes. The Batch Method was employed for dye removal experiments. Throughout the experimental procedure, the modification rate, initial dye concentration, and zeolite-dye ratios were systematically varied, and optimal parameters under these conditions were determined. Consequently, it was demonstrated that the modification of zeolite minerals with inorganic active substances can be utilized for the removal of pollutant dyes from aqueous solutions.
How to cite: Ünal, B. C., Ersoy, O., and Akkaş, E.: Investigation of Dye Removal from Water Using Zeolite Minerals Modified with Different Sodium Sources, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1023, https://doi.org/10.5194/egusphere-egu25-1023, 2025.
The toxicity of arsenic and its detrimental impact on human health have driven extensive research into effective removal methods (Smedley and Kinniburgh, 2002). Arsenate AsO43- can be efficiently sequestered from aqueous solutions by inducing the precipitation of mimetite (Pb₅(AsO₄)₃Cl), a stable and sparingly soluble phase with an apatite-like structure (Magalhães & Silva, 2003; Bajda et al., 2007; Bajda, 2010). This study introduces a novel application of lead-modified zeolite for arsenate removal, leveraging mimetite precipitation for efficient and environmentally sustainable water treatment. Pb bound to the zeolite surface exhibits optimal binding strength: strong enough to prevent the release of lead into water, yet weak enough to facilitate its reaction with arsenate and chloride ions present in solution.
This reaction led to the precipitation of mimetite directly on the surface of zeolite aggregates, ensuring efficient arsenic removal:
5Pb2+desorbed from zeolite + 3AsO43-contamination + Cl-supplied extra = Pb5(AsO4)3Cl precipitated on zeolite
The source of lead was a lead-modified natural clinoptilolite (ZEOCEM, Bystré, Slovak Republic), originally in its Ca form but transformed to Na-clinoptilolite after a 24-hour reaction in 2 M NaCl solution. This sodium form of clinoptilolite was then prepared by sorption of Pb²⁺ from solution, followed by intensive washing to remove excess Pb and desorption of loosely bound ions. 800 mg of Na-clinoptilolite was reacted with 40 mL of solution containing 4000 mg Pb/L at pH 4 for 24 hours, followed by washing with redistilled water and centrifugation (seven times) until Pb was below the detection limit of the Atomic Absorption Spectroscopy (AAS) method. The Pb-modified zeolite thus obtained, containing about 70 g of bound Pb per kg of zeolite, was subsequently reacted with arsenate solutions (500 mg of Pb-zeolite in 40 mL of solution containing 50 mg As(V)/L) in the presence of chloride ions (20 mg Cl/L) at pH 2 and 7 for up to 7 days.
At pH 7, arsenate levels decreased below the detection limit within 24 hours, while at pH 2, 95% of arsenate was removed. X–Ray Powder Diffraction (XRPD) and Scanning Electron Microscopy with Energy Dispersive Spectrometry (SEM-EDS) analyses confirmed the formation of mimetite, which precipitated on the zeolite aggregates, forming incrustations of distinct needle-like crystals up to 2 μm in length. Induced precipitation of mimetite produces a highly stable crystalline product, suggesting its potential for effective arsenate sequestration. This approach, with further testing in complex systems, holds significant promise for scalable and cost-effective arsenate remediation in contaminated waters.
References:
Bajda, T., Szmit, E., & Manecki, M. "Removal of As (V) from solutions by precipitation of mimetite Pb5(AsO4)3Cl." Environmental Engineering, (2007): 119-124.
Bajda, T. “Solubility of mimetite Pb5(AsO4)3Cl at 5–55 C.” Environmental Chemistry 7(3) (2010): 268-278
Magalhães, M. C. F., and Silva, M. C. M. „Stability of lead (II) arsenates.” Monatshefte fuer Chemie/Chemical Monthly, 134, (2003):735-743.
Smedley, P. L., and Kinniburgh, D.G. "A review of the source, behaviour and distribution of arsenic in natural waters." Applied geochemistry 17.5 (2002): 517-568.
How to cite: Stępień, E., Manecki, M., and Bajda, T.: Lead-modified zeolite for arsenate removal via mimetite (Pb5(AsO4)3Cl) precipitation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-895, https://doi.org/10.5194/egusphere-egu25-895, 2025.
Quantitative provenance analysis studies are instrumental in understanding the tectonic and climatic processes that are shaping Earth`s landscape. Although the most abundant mineral in the sedimentary system is quartz, almost all studies in provenance analysis investigate accessory minerals. Quartz contains various defects, intrinsic (mainly O related defects) or due to impurities. Some of these defects remain unchanged under ionizing radiation exposure while others are being transformed. Some of these defects are paramagnetic (e.g. E’, an unpaired electron at an oxygen vacancy site (≡Si·), peroxy intrinsic defect centers (≡Si-O-O⋅), nonbridging oxygen NBOHC, (≡Si–O⋅), Al related paramagnetic defects such as Al-hole, [AlO4]0, titanium impurity defects such as [TiO4/M+]0 where M+ is a cation, germanium defects ([GeO4]0, [GeO4/ M+] etc.) while others have the ability to emit light upon stimulation and were identified and characterised by techniques such as photoluminescence or cathodoluminescence (nonbridging oxygen, NBOHC, ≡Si–O⋅, oxygen deficiency center, ODC, ≡Si-Si≡ etc.). Based on the dynamics of radiation sensitive defects under irradiation, quartz can record the amount of ionizing radiation it has been exposed to since a resetting event. As such, quartz is successfully used for dating materials by thermoluminescence (TL) or optically stimulated luminescence (OSL) as well as by electron spin paramagnetic (EPR). Here we present multi-spectroscopic investigations (TL, OSL, EPR as well as hyperspectral resolved cathodoluminescence based on scanning electron microscopy) on quartz grains extracted from independently dated old to young quartz-bearing continental crustal sources, metamorphosed rocks versus their unmetamorphosed equivalents, as well as intrusive versus volcanic rocks and their derived sediments throughout the world. These investigations aim to prove that point defects in quartz have the capacity to carry genetic information and their modifications can provide evidence for antiquity, metamorphism (or lack thereof) as well as knowledge on transport, or recycling.
How to cite: Timar-Gabor, A.: Towards reading provenance from ubiquitous quartz by multi-spectroscopic investigations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-451, https://doi.org/10.5194/egusphere-egu25-451, 2025.
Seismological observation has revealed the ubiquitous presence of small-scale seismic scatterers with significant shear velocity reduction in the mid-lower mantle. In particular, more than 70% of seismic scatters were observed at depths of 700-1300 km, while 20% of them are distributed at 1300-1900 km depth. Only less than 10% of the seismic scatterers are detected at depths exceeding 1900 km. The phase transition from stishovite with rutile-type structure to post-stishovite with CaCl2-type structure of SiO2 in the subducted oceanic crusts was regarded as the main reason for these seismic scatterers. However, this phase transition for pure SiO2 is expected to occur at ~1800 km along the mantle geotherm, which is deeper than most observed seismic scatterers. Although the incorporation of Al and H into stishovite can effectively reduce the phase transition pressure, the combined effect of Al and H contents and temperature on the phase transition pressure of stishovite lacks necessary experimental constraints. In this study, we used Raman spectroscopy and single-crystal X-ray diffraction to provide comprehensive understanding on how the variation in chemical composition and temperature affect the post-stishovite transition pressure. According to our results, Al content variation ranging from 0 to 0.07 a.p.f.u with H/Al ratio of 1/3 in SiO2 can reasonably explain the depth distribution from 800 to 1900 km of the seismic scatterers observed at the circum-Pacific region. These results deepen our understanding on the complex features of mid-lower mantle seismic scatterers and corresponding dynamic processes.
How to cite: Yu, Y., Zhang, Y., and Mao, Z.: Unraveling the Complex Depth Distribution of the Seismic Scatterers in the Mid-Lower Mantle through Phase Transition of (Al, H)-Bearing Stishovite, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6476, https://doi.org/10.5194/egusphere-egu25-6476, 2025.
The stable pressure-temperature (P-T) ranges of metamorphic minerals are crucial for the reconstruction of geological history. Conventionally, phase diagrams were constructed using thermodynamic databases fitted to experimental measurements of e.g. heat capacity, elasticity, and volume. Kinetic processes such as phase transition and chemical diffusion cannot be directly accessed without knowing the corresponding parameters such as reaction energy barrier and diffusivity. In this work, we developed a machine learning interatomic potential trained with density functional theory (DFT) calculation for metamorphic minerals within Mg-Al-Si-O system. Molecular dynamics simulations were performed and combined with thermodynamic integration to obtain the free energy of a series of metamorphic minerals at high P-T conditions. The resulting phase relations match reasonably well with experimental data. We show that the aluminosilicate system is challenging due to the tiny energy difference among kyanite, andalusite and sillimanite. The coexistence P-T point for the three polymorphs is strongly dependent on the used exchange-correlation functionals. Silica system shows less dependency on different functionals and the complex polymorphs can be predicted with a good accuracy. Alpha-beta quartz transition is directly simulated using molecular dynamics without thermodynamic integration technique due to its low activation energy barrier. The developed interatomic potential has many potential usages, one being tested is the effect of nonhydrostatic stress on phase equilibrium. Preliminary result on alpha-beta quartz transition shows that the transition is mainly controlled by the mean stress, i.e. pressure. Under high differential stress up to 2 GPa, the transition pressure is shifted by only a few kbar. The finding has petrological implications on e.g. phase transition under confined environment such as mineral inclusion, or phase transition within shear zone under nonhydrostatic stress. More work will be focused on the nonhydrostatic stress effect on other minerals, the equation of state at high P-T conditions, and the effect on nuclear quantum effect on phase transition at lower temperature regime.
How to cite: Zhong, X., Li, Y., and John, T.: Prediction of phase diagram using machine learning interatomic potential and implication for equilibrium under nonhydrostatic stress, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11646, https://doi.org/10.5194/egusphere-egu25-11646, 2025.
Posters on site: Wed, 30 Apr, 14:00–15:45 | Hall X1
Megawite, a recently discovered perovskite-structured mineral with Ca(Ti0.07, Sn0.6, Zr0.33)O3, was identified in a xenolith. Its end members, CaTiO3, CaSnO3, and CaZrO3, represent GdFeO3-type perovskites (A2+B4+O3), which have garnered significant attention for their structural and physical properties. Among these, CaSnO3 stands out due to its exceptional optical and electrical properties, supported by its high physical and chemical stability. Despite its increasing applications, critical physical properties such as the elastic moduli (Cij) of single-crystal CaSnO3 have yet to be determined experimentally. Available data on CaSnO3 elasticity stems from polycrystalline measurements or computational predictions. This gap underscores the need for experimental determination of single-crystal elastic moduli better to understand its mechanical behavior and implications for future applications.
Here, we report the elastic moduli of single-crystal CaSnO3 perovskite measured using Brillouin scattering at ambient conditions. Crystals of CaSnO3 were synthesized at 1200 °C over 24 hours from a starting mixture of CaCl2 and SnO2 in a 2:1 molar ratio. Four high-quality crystals were selected for Brillouin scattering measurements. Full elastic moduli were derived via least squares regression of sound velocity data against the Christoffel equation. The obtained values for the elastic moduli include longitudinal moduli (C11, C22, C33) ranging from 270 to 290 GPa, shear moduli (C44, C55, C66) between 90 and 98 GPa, and off-diagonal moduli (C12, C13, C23) ranging from 100 to 120 GPa. These measurements' aggregate bulk modulus, shear modulus, and sound velocities align well with previous polycrystalline results obtained through ultrasonic interferometry (Kung et al., 2001; Schneider et al., 2008).
A key step in Brillouin scattering data analysis is the establishment of an initial Cij model. For a new material such as CaSnO3, setting up an effective starting model requires experience. In this study, the starting Cij model was derived from density functional theory (DFT) computations to serve the purpose. Elasticity and electronic ground states were calculated using the CASTEP code integrated within the Materials Studio software package. These calculations employed LDA, GGA, and mGGA functionals, with norm-conserving and ultrasoft pseudopotentials modeling electron-ion interactions. The computationally predicted Cij values served as the initial input for data fitting. The final best-fit Cij model was determined by minimizing residual differences across iterative fitting steps. The close agreement between experimental and computational results highlights the utility of computational predictions as a starting point for Brillouin scattering analyses.
This study presents the first experimental determination of the elastic moduli for single-crystal CaSnO3 perovskite, supported by computational insights. The integration of experimental and computational approaches offers a robust framework for characterizing the mechanical properties of new materials. Our findings contribute to the broader understanding of perovskite materials, with implications for geosciences and advanced material applications.
How to cite: Kung, J., Hua, F. T. S., Su, W., and Zhang, J.: Elastic Moduli of Single-Crystal CaSnO3 Perovskite, end-member of Megawite: Bridging Experimental and Computational Approaches, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5577, https://doi.org/10.5194/egusphere-egu25-5577, 2025.
The present study examines the effect of metamorphism on point defects in quartz. A granite sample with crystallization age of ~460 Ma (Albesti granite, Romania) and its metamorphic equivalent were used for the analysis. This sill-like granitoid occurs close to a ductile shear zone (locally named Bughea shear zone) of presumed Variscan age; the granitoid is exposed as relatively undeformed away from the shear zone as well as highly strained into a mylonitic fabric, when caught into the shear zone. Mineralogical differences were also observed, the metamorphic sample exhibiting lower quartz content and reduced grain strength. The point defects in quartz were characterized using thermoluminescence (TL), optically stimulated luminescence (OSL), electron spin resonance (ESR), scanning electron microscopy coupled with cathodoluminescence (SEM-CL) and Raman spectroscopy.
ESR data showed the presence of E’ (an unpaired electron at an oxygen vacancy site (≡Si·), Al-related defects ([AlO4]0) and peroxy (≡Si-O-O·) in both the samples with increase of these centres in the metamorphic sample, especially in the case of the latter. TL measurements showed four peaks (110, 160, 280, 380 °C) in both samples, though TL intensity was 40% lower in the metamorphic quartz. The OSL decay curves were dominated by fast component for un-deformed sample and the OSL intensity of the metamorphic quartz was approximately 60% lower than that of un-deformed granite. The OSL dose-response curve (DRC) is well represented by a sum of two saturating exponential functions. The DRC of metamorphic granite exhibited higher uncertainties, due to its low signal. The DRC shapes before and after heating were nearly identical for both samples. SEM-CL analysis showed emission in blue (~450 nm) and red region (~650 nm; attributed to NBOHC (≡Si–O·)). The CL emission of metamorphic quartz was 65% lower than that of un-deformed quartz. Raman spectroscopy showed narrowing of quartz bands in the region of 100 to 500 cm⁻¹, reflecting the shortening of the O-Si-O bond (463 cm⁻¹) and lattice compression (125 and 204 cm⁻¹) during metamorphism. The increase at the 1030 cm⁻¹ peaks indicates the high aluminium-to-silicon ratio which concords with the ESR measurements.
These findings provide new insights into mineralogy and quartz point defect dynamics under metamorphic conditions, with implications for geological processes. At the conference, detailed results and their implications will be presented.
Acknowledgement: This research is funded by European Research Council ERC grant PROGRESS-CoG “Reading provenance from ubiquitous quartz: understanding the changes occurring in its lattice defects in its journey in time and space by physical methods”
How to cite: Devi, M., Tóth, Z.-R., Grecu, S.-C., Nesterovschi, I., Constantin, D., Ducea, M. N., Pinzaru, S. C., and Gabor, A. T.: Effect of Metamorphism on the Point Defects in Quartz: Characterization using Different Spectroscopic Techniques , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5922, https://doi.org/10.5194/egusphere-egu25-5922, 2025.
Point defects in quartz and their response to irradiation hold geological significance but are not well understood. They can be analyzed using methods like optically stimulated luminescence (OSL), electron spin resonance (ESR), and scanning electron microscopy with cathodoluminescence (SEM-CL). This study examines point defects in a granite sample (~1.4 Ga crystallization age, ~20–23 Ma cooling age) from the Catalina Metamorphic Core Complex, southwestern USA, part of a Proterozoic anorogenic granitic province.
Defects analyzed include intrinsic ones (e.g., O-vacancies, Si vacancies, and nonbridging oxygen centers) and impurity-related defects (e.g., [AlO4]⁰ and [TiO4/M⁺]⁰). ESR identified E', peroxy, Al-, and Ti-related defects, with Al and Ti defects showing higher intensities. The Al-hole center increased exponentially with dose up to 40,000 Gy, while the Ti-electron center showed a nonmonotonic trend, peaking at 10,000 Gy and then decreasing, consistent with Benzid and Timar-Gabor (2020) and Woda and Wagner (2007). Oxygen-related defects were weak and generally dose-independent. OSL decay was dominated by a fast component, and SEM-CL showed strong blue emissions (~450 nm) and weak red emissions (~650 nm, related to NBOHC), confirming Ti-related defect dominance.
One can explain the features of luminescence and ESR signal in quartz, especially their dependence on the irradiation dose, by modelling the charge transport processes during its exposure to high-energy radiation or light. So far, models based on the band theory used in simulations of the luminescence in quartz (e. g. Bailey, 2001) have not considered that, next to electrons, ions also carry the charge in this material. Ionic conduction in quartz is primarily related to interstitial light metal cations M+. These ions provide a charge balance in the lattice disturbed by substituting a silicon atom with an aluminium atom at the crystallization stage. Radiation generates free electrons and holes, causing local potential changes that induce cation transport in the crystal. Ionic conduction in quartz requires, therefore, considering, in the modelling, both electronic transitions and changes in the state of ions from bound to free and vice versa.
A kinetic model was developed with differential equations describing M⁺-binding centers (Al and Ti), electronic states, and free electron and ion concentrations. The results, which provide insights into point defect dynamics in granitic quartz, will be discussed at the conference, offering new perspectives.
References:
Benzid, K., Timar-Gabor, A., 2020. Phenomenological model of aluminium-hole ([AlO4/h+]0) defect formation in sedimentary quartz upon room temperature irradiation: electron spin resonance (ESR) study, Radiation Measurements, 130,106187.
Woda, C., Wagner, G. A., 2007. Non-monotonic dose dependence of the Ge-and Ti-centres in quartz. Radiation measurements, 42(9), 1441-1452.
Bailey, R. M., 2001. Towards a General Kinetic Model for Optically and Thermally Stimulated Luminescence of Quartz. Radiation Measurements 33: 17-45.
Acknowledgement: This research is funded by European Research Council ERC grant PROGRESS-CoG “Reading provenance from ubiquitous quartz: understanding the changes occurring in its lattice defects in its journey in time and space by physical methods”
How to cite: Tóth, Z.-R., Devi, M., Pawlak, N., Grecu, S.-C., Constantin, D., Dave, A. K., Ducea, M. N., Chruścińska, A., and Timar-Gabor, A.: Understanding defect dynamics under irradiation in quartz: case study of a 1.4 Ga granite sample investigated by multispectroscopic methods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5985, https://doi.org/10.5194/egusphere-egu25-5985, 2025.
Despite being one of the purest minerals, quartz presents different types of defects, intrinsic or due to impurities, that might contain important genetic information. Its common occurrence is making it a promising tool for provenance studies. This study explores scanning electron microscopy (SEM) coupled with cathodoluminescence (CL) wavelength resolved spectroscopy for investigating luminescence emissions of quartz sourced from rocks of different types, spanning diverse geological ages.
All examined samples display two distinct broad emissions: a blue emission centred at approximately 440 nm (2.7 eV) and a dominant red emission around 650 nm (1.9 eV). The 650 nm (1.9 eV) emission present in quartz samples is attributed to the non-bridging oxygen hole centres (NBOHC). The formation of NBOHCs involves multiple mechanisms, including processes associated with radiation damage in quartz (intrinsic mechanisms) as well as hydrogen- or alkali-passivated precursor defects (extrinsic mechanisms) (Skuja et al., 2020). Making a distinction between the two mechanisms of NBOHC formation is a challenging task that has been rarely adressed. In the long run, we aim to demonstrate that NBOHC defects, which may be inherent to a certain extend since crystallization, could serve as reliable indicators of age, particularly for similar types of samples.
Here we study the dynamics of this defect under 15 keV electron irradiation in SEM. The samples were irradiated for different exposure times. Preliminary results indicate a saturating exponential growth of the red emission. While a growth of the NBOHC under irradiation was previously reported in the literature (e.g. Götze et al., 2021), here we describe this increase in a quantitative manner.
The observed behaviour is well-described by equation S(t) = S(0) * (1- exp(-(t-t0)/tc)).
Here, tc represents the critical time, a measure of the time required for the signal to increase by a factor of 1/e. By determining tc, a characteristic saturation time, hence dose can be calculated. While experiments are still in progress, for our experimental setup, tc values range from 300 to 500 s, depending on the sample. The maximum intensity is not showing significant variation across most samples, with a significant exception for the oldest sample investigated. A noteworthy observation is the non-zero value of t0, the time intercept, which suggests that NBOHC exists in the quartz samples since crystallization, before irradiation. In the end, quantifying the exposure to the electron beam in terms of radiation dose (energy delivered per unit mass expressed in Gy) is attempted for facilitating direct comparisons with results obtained by other experimental techniques such as electron paramagnetic resonance or optically stimulated luminescence.
Acknowledgement: This research is funded by European Research Council ERC grant PROGRESS-CoG “Reading provenance from ubiquitous quartz: understanding the changes occurring in its lattice defects in its journey in time and space by physical methods”
References:
Skuja, L., Ollier, N., Kajihara, K. 2020. Luminescence of non-bridging oxygen hole centers as a marker of particle irradiation of α-quartz. Radiation Measurements, Volume 135, 106373.
Götze J., Pan Y. & Müller A. 2021. Mineralogy and mineral chemistry of quartz: A review. Mineralogical Magazine. 85(5):639-664. DOI:10.1180/mgm.2021.72
How to cite: Grecu, Ș.-C. and Timar-Gabor, A.: Characterization of SEM-CL red emission in quartz from various types of rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6869, https://doi.org/10.5194/egusphere-egu25-6869, 2025.
The primary source of clay for ceramic producers in Turkey has historically been the clay extracted from the Şile region and imported from Ukraine. However, the depletion of existing resources and the increase in logistics costs have prompted the sector to explore alternative raw materials. In this context, the stratified sepiolite deposits in Sivrihisar region (Eskişehir, Türkiye) have garnered attention. While these deposits have been utilized in industrial applications, such as cat litter and exported overseas, since the 1970s. The limited physico-chemical properties of sepiolite clay have precluded sufficient investigation into its use in ceramic recipes to date.
Sepiolite formations have been identified within the sedimentary succession of Sakarya Formation Miocene in age. Sepiolite formation is believed to have been sourced from ophiolites, Paleocene-Eocene aged granitoids and marbles. The mineral deposits, which were formed in the lacustrine basins that emerged during tectonic movements, have been converted into sepiolite and dolomite sepiolite deposits in both alkaline and salty environments. However, the absence of lateral continuity in these deposits suggests that their economic viability may be constrained.
This study aims to investigate the potential application of sepiolite and dolomite sepiolite deposits in the Kurtşeyh and Oğlakçı regions of Sivrihisar in the production of wall and floor tiles. The methodology includes geological mapping in both regions, the preparation of stratigraphic sections, and systematic sampling together with the chemical, mineralogical and technological analysis. Geological observations indicate that the sepiolite succession occur in three distinct forms: as pure sepiolite, sepiolite-bearing dolomite, and dolomite-bearing sepiolite. XRD analysis revealed the raw materials to consist of sepiolite ± dolomite ± calcite ± montmorillonite ± palygorskite ± organic ingredients. XRF analysis indicated the prevalence of CaO, SiO2, and MgO in these clays, with components such as Al2O3 and Fe2O3 being secondary.
In the laboratory, the thermal properties of the samples were investigated through the application of firing processes. Wall tiles were produced through a 40-minute firing process at 1125°C, while floor tiles underwent a 67-minute firing process at 1185°C. The technological properties of the materials, including density, shrinkage, water absorption, dry strength, and color, were evaluated. The results obtained demonstrated that sepiolite, particularly dolomite sepiolite, can be utilised as an alternative for Istanbul (Şile) and Ukraine clays in ceramic formulations. The adding of 10% of sepiolitic clays into the ceramic mixture exhibited performance that was commensurate with standard production processes.
In conclusion, sepiolite and dolomite sepiolites have been identified as a potential alternative raw material for the ceramic industry in the Kurtşeyh and Oğlakçı regions of Sivrihisar. However, further detailed field studies and industrial-scale trials are required to ensure economic and logistical sustainability.
How to cite: Pocan, H., Doğu, M. M., Yüksel, S., Genç, Ş. C., Kayacı, K., and Yıldırım, Y.: Investigation of Oğlakçı and Kurtşeyh Sepiolites (Eskişehir, Türkiye): As Common Clay Alternatives and Possibilities of Use in Terms of Ceramic Tile Production, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9472, https://doi.org/10.5194/egusphere-egu25-9472, 2025.
Minerals are key markers of the multi-stage processes that occurred in their environment of formation and evolution. We present three micro textural and chemical studies of minerals from lherzolites in the French Massif Central.
-1- Carbonate-bearing mantle xenoliths are interesting as highly mobile carbonate melts are prominent metasomatic agents of the mantle. Here, carbonate fills globular vesicles in composite reaction zones that contain secondary clinopyroxene, olivine, spinel, ± plagioclase and glass. The secondary clinopyroxene and olivine indent or are included in the carbonate crystals. The carbonate is a REE- and alkali-poor calcite with low MgO <1 wt.%.
The presence of rounded vesicles of carbonate is usually interpreted as an evidence for silicate-carbonate liquid immiscibility, but alkali-free immiscible carbonates cannot be almost pure calcite. Here the textural and composition characteristics of carbonates rule out their origin as quenched carbonatitic melts or immiscible carbonate liquids and favor an origin as crystal cumulates from mantle-derived alkali-carbonate melts.
The co-precipitation of carbonate and secondary minerals occurs near the base of the crust. The injection of small amounts of a carbonate-rich melt occurred at mantle level shortly before the eruption to preserve the calcite crystals.
-2- Here we present Li abundances and isotopes data of co-existing silicates in anhydrous and amphibole-bearing lherzolites. Li abundances increase in all phases from the amphibole-bearing lherzolites, but deviate from the trend of equilibrium partitioning between phases with a preferential Li uptake in clinopyroxene. The correlation between Li and REE elements in clinopyroxene suggests that Li and REE were carried by the same silicate melt.
In the amphibole-bearing lherzolites the cpx d7Li (‰) values show large intra-grain variations. These variations do not provide evidence for different sources but likely result from high temperature diffusion-related Li fractionation during metasomatism by the silicate melt undergoing compositional changes as it percolates through the lherzolites.
The preservation of both the Li isotope kinetic fractionation in minerals and isotopic heterogeneities implies that the Li exchange event occurs just before the extraction of the xenoliths from the mantle.
-3- Glass-bearing pockets in peridotite xenoliths are usually studied for elucidating the origin of the infiltrating agent. We present here a chemical study of glass developed around spinels. We do not discuss the origin of the metasomatic agent but show that 1) the modification of the structure of the percolating melt is due to the accommodation of elements produced by the dissolution of minerals and (2) how this process could modify the oxidation state of the melt.
Spinel-derived Al3+ ions are first accommodated to the melt network as network-modifiers and secondly as network-formers using K+ ions as stabilizators within the tetrahedral site. The transfer of K+ ions (extracted from the aqueous fluid upon melt dehydration) from the aqueous fluid to the melt network is counterbalanced by an inverse transfer of CaO molecules that form crystalline phases exsolved upon eruption.
Spinel corrosion generates melt oxidation through dehydrogenation reactions resulting in the formation of Al3+ and Fe3+ anionic complexes within the melt network.
How to cite: Wagner, C., Boudouma, O., Fialin, M., and Deloule, E.: Minerals as key tools for characterizing multi-stage processes in the lithospheric mantle., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13622, https://doi.org/10.5194/egusphere-egu25-13622, 2025.
The central Yukon Territory is renowned for its exceptionally abundant beryl occurrences. In 2003, widespread medium-blue aquamarine mineralization was discovered in the Black River Batholith, south-central Yukon. This aquamarine occurrence is notable because it is hosted in granodiorite, rather than being associated with pegmatites. Four distinct beryl occurrences have been documented in the batholith: (1) beryl with tourmaline, separated from the granodiorite by an aplite zone; (2) beryl with tourmaline bordering the granodiorite, with no aplite; (3) a set of beryl-quartz veins devoid of tourmaline, striking 70° and dipping 60° south; and (4) a second set of veins striking 315° and sub-vertical.
This study aims to: first, compare the different types of aquamarine occurrences and identify distinguishing features; second, compare this occurrence with the Tsa Da Glisa emerald deposit (15 km northeast) and the true blue aquamarine locality (150 km northwest); and third, determine an accurate age for the Black River Batholith and compare it with nearby intrusions.
The Black River Batholith, in the Finlayson Lake map area, is an Eocene-aged granitic intrusion emplaced within Cambrian to Lower Cambrian sedimentary rocks of the Kechika Group and Rosella Formation. It forms part of the geologically complex Canadian Cordillera, an orogenic belt formed by terrane accretion onto the Laurentian craton. Structurally, the batholith lies between the Tintina Fault to the north and the St. Cyr Thrust Fault to the southeast, with an elongated morphology aligned with these structures. These features suggest a complex tectonic evolution, potentially influenced by post-accretionary transcurrent faulting.
The batholith is predominantly peraluminous, consisting of K-feldspar-phyric monzogranite to granodiorite, with accessory minerals like biotite, muscovite, and tourmaline. Previous geochronological investigations yielded discordant ages, with K-Ar dating of biotite ranging from 46.9 ± 2.6 Ma to 68 Ma. Nearby lithologically similar intrusions yielded K-Ar ages of 70 to 100 Ma, indicating either a distinctive emplacement history for the Black River Batholith, deficiencies in earlier dating methods, or subsequent reheating events.
This study employs U-Pb zircon geochronology and whole-rock geochemical analysis to clarify the temporal and compositional relationships of the Black River Batholith with nearby intrusions and test its affiliation with the Cassiar Suite. Geochemical analysis of beryl-bearing and non-beryl-bearing granitoids will help delineate the chemical provenance of the beryl occurrences. Additionally, we will use SEM and EPMA to investigate compositional variations among beryl occurrences and zoning within individual beryl crystals, providing insights into their chemical affinities and source divergences. This integrated approach aids in reconstructing the Black River Batholith’s emplacement history and enhances our understanding of the region's magmatic evolution.
This study is significant because it addresses long-standing uncertainties regarding the batholith’s emplacement age, its relationship to nearby intrusions, and the origins of its unusual beryl occurrences. These occurrences have not been studied in detail before and may provide valuable insights into magmatic-hydrothermal processes in the region.
How to cite: Groat, L., Ozyalcin, C., and Breasley, C.: Aquamarine Mineralization in the Black River Batholith, Yukon Territory, Canada, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15015, https://doi.org/10.5194/egusphere-egu25-15015, 2025.
The albite breakdown reaction to jadeite and quartz is frequently utilized for the calibration of piston-cylinder apparatuses due to its well-established and highly precise equilibrium conditions. In nature, jadeitic pyroxene serves as an indicator for high-pressure conditions during metamorphism. Quite a few granites can be found in association with mafic eclogites, so that jadeite + quartz would be expected to be common. While jadeite has been documented in a number of locations, it is often absent in continental high-pressure rocks. Several possible explanations for the absence of jadeite have been proposed; a) the nominally dry reaction may be kinetically too slow in the absence of free water in the system; b) complete retrogression of jadeite paragenesis by later lower pressure metamorphism, or c) that the pressure gradients between mafic eclogites and granites lead to P-T conditions that prevent jadeite formation.
This experimental study aims to determine whether jadeite can form without free water or if slow reaction kinetics hinder its formation. Isochemical phase diagrams have been calculated within the NCKFMASH system to model the water acitivity. It is shown, that biotite breakdown at elevated P-T conditions may provide free water on the grain boundaries even at nominally dry experimental conditions, thus increasing water activity and passively promote jadeite formation. To investigate this effect, three sets of piston-cylinder experiments are conducted using natural granite (100-400 µm). The experiments were annealed just outside the jadeite stability field to eliminate grain boundary water introduced by the powder, before exposing them to eclogite facies conditions. Kyanite is added in some experiments to induce the formation of white mica, thereby reducing the water activity by adsorbing the water in the crystal lattice.
The results of this study will elucidate whether jadeite formation is kinetically inhibited in the absence of free water. If jadeite forms only when free water is present during the reaction, it can be concluded that indeed sluggish kinetics, driven by the absence of free water, impede jadeite formation in high-pressure metagranites.
How to cite: Abel, A., Müller, T., Sorger, D., and Baumgartner, L.: The role of water on the reaction kinetics of a nominally dry reaction: Experimental study on the albite breakdown to form jadeite and quartz, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16735, https://doi.org/10.5194/egusphere-egu25-16735, 2025.
Water pollution arises not only from anthropogenic sources but also from natural contaminants, which can cause equally significant harm. Among these natural pollutants, mycotoxins – secondary metabolites produced by fungi – stand out due to their widespread occurrence and the serious health risks they pose to both humans and animals. Zearalenone (ZEN), one of the most prevalent mycotoxins, is known to induce oxidative stress, DNA and mitochondrial damage, apoptosis, and alterations in gene expression, emphasizing its toxicological relevance. To address ZEN contamination efficiently, economically, and without producing secondary pollutants, a UV-driven photodegradation approach was used.
Our research focused on the impregnation of the mineral supports with 20 wt% of semiconductors, including TiO2, GCN, and their 1:1 mixture. The selected mineral supports included natural kaolinite, purified halloysite, and synthetic kaolinite nanotubes. The resulting materials were evaluated for their efficiency in removing ZEN under both UV and visible light. Their performance was further assessed in the presence of a co-occurring mycotoxin, deoxynivalenol (DON), as well as under varying pH levels and ionic strengths of the solution. Most importantly, extensive electrochemical studies were conducted to elucidate the mechanisms underlying their functionality, with particular attention to their photocatalytic properties.
The most effective materials – kaolinite nanotubes combined with GCN and TiO2/GCN – achieved ZEN removal efficiencies of 98.8% and 97.7%, respectively, from an initial concentration of 10 ppm after just 25 min of irradiation. While the kinetics of ZEN removal under visible light were noticeably slower than under UV light, the results remain promising when compared to the literature. Experiments conducted under varying pH conditions highlighted the role of ZEN protonation in the removal process. The results revealed that DON was not removed under the tested conditions, and its presence slightly reduced the efficiency of ZEN degradation. Scavenger experiments, supported by electron paramagnetic resonance (EPR) with spin-trapping measurements, identified O2•- and •OH radicals as the key species involved in the photodegradation process. Time-resolved photoluminescence (TRPL) lifetime measurements demonstrated a prolonged carrier lifetime in materials containing kaolinite nanotubes and GCN. This finding is consistent with the chopped light voltammetry (CLV), which indicated the presence of traps within the structure of the photocatalyst. These results provide strong evidence for the beneficial role of mineral supports, particularly kaolinite nanotubes. Furthermore, electrochemical impedance spectroscopy (EIS) suggested enhanced mobility of photogenerated holes at the interface between the mineral support and GCN, further reinforcing the positive impact of the mineral supports.
The photodegradation pathways of ZEN, proposed based on identified radical formation and UHPLC-ESI-MS/MS analysis, involved a series of reactions, including hydrolysis and, most notably, oxidation and cleavage. These processes lead to the formation of several intermediate products with both lower and higher molecular masses compared to ZEN. Their chronic and acute toxicity was evaluated using dedicated ECOSAR software.
This project was supported by the National Science Centre Poland, under a research project awarded by Decision No. 2021/43/B/ST10/00868.
How to cite: Dziewiątka, K., Matusik, J., Herber, M., Hill, E. H., and Kuc, J.: Removal of zearalenone mycotoxin with kaolin group-based photocatalysts: exploration of mechanisms and photodegradation pathways, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17928, https://doi.org/10.5194/egusphere-egu25-17928, 2025.
Cosmic processes, geological processes and human activities on Earth introduce dust, gases, and aerosols into the atmosphere. Various reactions between them take place, including photochemical reactions, and new compounds are formed. Particulate matter is transported in the atmosphere sometimes over global distances and remains suspended even for many years. The phase composition of atmospheric dust, on a par with its chemical and isotopic composition, are the “fingerprints” for determining its source, transformation processes and health effects. Mineralogical analysis of the presence and distribution of particles in the atmosphere, their quantity, diversity and routes of transport is a powerful tool in modern studies of global environmental transformations.
The term aeromineralogy was proposed for that part of mineralogy that addresses such issues (Manecki, 1976, Manecki et al., 1984), following the example of biologists who called aerobiology the branch of biology that studies the aeroplankton floating in the atmosphere. To study the mineral and chemical composition of atmospheric dust, aeromineralogy uses specific methodology: specific tools for collection and separation of the particles followed by microscopy (polarizing microscopes, electron microscopes, atomic force microscopy, etc.), diffraction methods (X-ray diffractometry, electron diffraction, EBSD, etc. ), different varieties of microprobes for chemical and isotopic microanalysis, spectroscopy for determination of H2O, OH, and organic matter (IR, Raman, etc.) and many other less classical methods from the mineralogist workbench. Comprehensive analyses of airborne particulate matter are routinely performed for both research and monitoring purposes, for health protection, both indoors and outdoors, since not only the size of inhaled particles, but also their phase composition accounts for potential hazards or health effects (see for example Peña-Castro et al., 2023; Puławska et al., 2021).
Therefore, it is advisable to more broadly publicize the name aeromineralogy for the promotion of the contribution, role, and specificity of mineralogical research and analytical methods in everyday applications of occupational health and safety practice, in the monitoring of contemporary global environmental changes, the circulation of atmospheric particles on Earth, and in studies of cosmic matter (see for example Genge et al., 2020).
Genge et al., 2020. Micrometeorites: Insights into the flux, sources and atmospheric entry of extraterrestrial dust at Earth. Planetary and Space Science. https://doi.org/10.1016/j.pss.2020.104900.
Manecki, A. 1976. Aeromineralogy, mineralogy of atmospheric dust. Mineral. Polon., vol. 7, no. 2.
Manecki A. (ed.) 1984. Transport and input of air pollutants in the Niepołomice Forest area. In: Forest Ecosystems in Industrial Regions. Ecol. Stud., 48. Springer.
Peña-Castro et al., 2023. A critical review of asbestos concentrations in water and air, according to exposure sources. Heliyon. https://doi.org/10.1016/j.heliyon.2023.e15730.
Puławska et al., 2021. Origin, distribution, and perspective health benefits of particulate matter in the air of underground salt mine: a case study from Bochnia, Poland. Environ Geochem Health, https://doi.org/10.1007/s10653-021-00832-2
How to cite: Manecki, M. and Manecki, A.: Aeromineralogy - mineralogy of solid particles in the atmosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17164, https://doi.org/10.5194/egusphere-egu25-17164, 2025.
Zeolites form in various geological environments; among all, volcanic materials are the most important zeolite precursors. In this study, zeolites were synthesized by hydrothermally treating the volcanic material. The fine powdered pumice sample, used in this study, is one of the pyroclastic products of the Central Anatolian Volcanic Province (CAVP). This study mainly focused on the phase-transition and characteristics of zeolites formed under different reaction agent contents in a hydrothermal synthesis reactor. The products of the hydrothermal treatment were characterized using various analytical techniques, such as X-ray diffraction, scanning electron microscopy, and FTIR measurements. The hydrothermal treatment was performed with NaOH (1M, 2M, and 3M) and 1M KOH reaction agents at 150 ºC for 8 to 16 h. Meanwhile, diatomite is specifically utilized in this study to observe its impact on the reaction and to increase the silica content of the starting material. The crystallinity and characteristics of the reaction products were affected by the molar concentration and type of the reaction agents. The products mainly consist of analcime, chabazite, Na-phillipsite, and Na-P1. The alumina-silicate gel produced by the reaction of 2M NaOH with natural volcanic material has the potential to transform into chabazite and Na-P1. With the increase in molar concentration of NaOH, more sodium participates in the reaction to form zeolite phases of analcime, Na-P1, and Na-phillipsite. Following the addition of diatomite to the reaction with 3M NaOH, it has been noted that Na-Al-Si-rich gel has been produced beside analcime, Na-P1, and Na-phillipsite. The results obtained in this study showed that natural volcanic material led to the formation of gels under different alkaline activation conditions, which seemed to control the generation of zeolites.
How to cite: Akın, L. and Çubukçu, H. E.: Phase transformation and characteristics of hydrothermal zeolites formed under alkaline conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11641, https://doi.org/10.5194/egusphere-egu25-11641, 2025.
