Feldspar Samples Research Articles

Investigating thermoluminescence signal saturation in quartz and feldspar using emission spectrometry

Luminescence-based thermometry and dating often requires determination of the saturation level for specific signals and the corresponding dose. However, previous studies found non-monotonic dose responses for some monochromatic thermoluminescence (TL) and optically stimulated luminescence (OSL) signals from quartz as well as spectral overlap of emission bands, substantially complicating data interpretation. Therefore, the present study examines (1) the variability in the TL emission spectrum of quartz and feldspar from bedrock and sediment of different provenances and, (2) the saturation characteristics of the blue emission band for both quartz and feldspar in the dose range from 0.25 kGy to 50 kGy. The experimental results confirm differences in the spectra which appear to be characteristic of their geological origin and chemical composition. Spectral analysis shows that in the temperature range 175–220 °C the blue emission band at ∼2.5 eV dominates over other bands for all quartz samples studied. A broad UV-blue TL signal peaking at ∼2.5−3.0 eV and composed of probably three overlapping, individual bands is characteristic for K-feldspar, while one Na-feldspar exhibits an additional band at ∼2.2 eV.In the studied dose range, the emissions at ∼2.5 eV and ∼2.6 eV increase as a function of dose up to 6 kGy for both quartz and feldspar. A difference in dose response was observed for high doses (>6 kGy) where feldspar samples reached a stable saturation level while for quartz the blue emission band intensity decays until 50 kGy after having attained a maximum. Our results suggest the suitability of feldspar TL for palaeothermometry and thermochronometry from the perspective of signal saturation characteristics. However, the spectral overlap of several bands in the UV-blue emission requires careful optical filter selection to isolate the signal of interest. The non-monotonic dose response of the ∼2.5 eV emission of quartz around 200 °C glow curve temperature probably precludes its use for temperature sensing based on relative trap saturation levels.

Exploring the use of averaged thermal kinetic parameters in luminescence thermochronometry

In luminescence thermochronometry, the thermal stability of feldspar minerals is conventionally constrained from isothermal decay experiments. However, despite recent refinement of the measurement protocol, measurements take several days and are routinely done for each individual sample. Following that most other thermochronometric methods usually use only a single reference set of thermal kinetic parameters, and that recent studies on direct physical probing of feldspar sample properties have shown that trap depth and band-tail width are broadly similar despite large variations in chemical composition, we sought to optimise luminescence thermochronometry measurements by exploring whether a single set of thermal kinetic parameters can describe luminescence thermal decay in feldspar. We explored the effect of using averaged thermal kinetic parameters rather than sample-specific thermal kinetic parameters to model luminescence signal accumulation under different thermal conditions. A set of K- and Na-feldspar minerals extracted from all over the world were analysed after being measured with a multi-elevated temperature protocol, comprising four different IRSL signals at 50, 100, 150, and 225 °C. Comparisons were done between the thermal kinetic parameters of each IRSL signal depending on different variables such as geographic region, transect, lithology, or mineralogy of the analysed feldspar grains. Even though it is not possible to generalise the thermal kinetic parameters between IRSL signals measured at different temperatures, the variance between the thermal kinetic parameters of different samples measured at the same IRSL temperature is consistent with the uncertainties on the individual parameters (i.e., <2–10%), suggesting that averaged, rather than sample-specific values may be appropriate. We then explored the effect of using these averaged parameters to model luminescence signal accumulation under different synthetic and natural thermal conditions. For our dataset, results show minimal impact on the obtained cooling histories and exhumation rates. We therefore propose the use of averaged rather than sample-specific thermal kinetic parameters for rapid investigation of luminescence thermochronometry samples. Based on careful initial characterisation of a few samples to verify the validity of using averaged thermal kinetic parameters, this would reduce measurement times by ca. 50% (i.e., 3–4 days per sample), allowing higher resolution sampling and measurement.

The Analysis of feldspar characteristic as ceramic material at Mount Ragas, Jepara, Central Java

The ceramic industry in Indonesia is growing rapidly so it needs a lot of raw and mixture materials for ceramics. One of the materials needed in the manufacture of ceramics is feldspar. At Mount Ragas, located in Clering Village, Donorojo, Jepara, Central Java, there are feldspar deposits which have the potential to supply the demand of the ceramic industry. The purpose of the study was to determine the geological conditions, mineralogical composition, chemical composition and characteristic of feldspar in ceramic industry. The research methods used were geological mapping, petrographic analysis and XRF geochemical analysis. The lithology of research area consists of andesite and alluvium deposits. Andesite is composed of plagioclase (andesine), alkali feldspar, quartz, hornblende, pyroxene and opaque mineral. The chemical composition of feldspar consists of SiO2 (61.03-65.01%), Al2O3 (20.23-22.5%), K2O (5.27-5.52%), Na2O (4.65-5.1%), CaO (0.43-0.65%), Fe2O3 (0.61-2.13%), MgO (<0.01%), MnO2 (<0.01%), TiO2 (0.09-0.11%), Cr2O3 (<0.01%), LOI (1.65-1.73%). Based on SNI No. 1145-1984, no samples meet the requirements for porcelain materials, only sample SMP-05 meets the requirements for sanitary materials and samples SMP-04, SMP-05 and SMP-06 meet the requirements for pottery material. Based on the standard from PT Semarang Mineral Pembangunan, feldspar samples that meet the requirements for glass materials are SMP-04 and SMP-05 and samples that meet the requirements for ceramic materials are SMP-01, SMP-02, SMP-03 and SMP-06.

Identification of Some Gem-Quality Red and Green Feldspars

Sunstone is a member of the feldspar group. Natural sunstones from Oregon exhibit unique optical effects and hold significant market value. However, since 2008, there has been a persistent issue of diffused red feldspars masquerading as natural sunstones in the market, severely undermining consumer confidence in purchasing natural sunstones. Fluorescence characteristics under 305–335 nm ultraviolet excitation are considered an effective method for distinguishing copper-diffused red feldspars from natural sunstones. In this paper, through detailed analysis and testing of ten market-acquired red and green feldspar samples, including UV-vis spectra, microscopic characteristics, fluorescence spectra, and chemical compositions, we validate the efficacy of fluorescence characteristics in identifying copper-diffused feldspars. The results verify the widespread prevalence of copper diffusion treatment in market-acquired red and green feldspars, shedding light on their treatment history and providing valuable insights for jewelry consumers. This research not only enhances our understanding of sunstone treatments but also strengthens the reliability and applicability of fluorescence spectroscopy in gemstone identification, offering promising prospects for its broader adoption in the jewelry market.

Technical note: Darkroom lighting for luminescence dating laboratory

Abstract. An optimal lighting setting for the darkroom laboratory is fundamental for the accuracy of luminescence dating results. Here, we present the lighting setting implemented in the new Luminescence Dating Research Laboratory at Stony Brook University, USA. In this study, we performed spectral measurements on different light sources and filters. Then, we measured the optically stimulated luminescence (OSL) signal of quartz and the infrared stimulated luminescence (IRSL) at 50 ∘C (IR50) as well as post-IR IRSL at 290 ∘C (pIR-IR290) signal of potassium (K)-rich feldspar samples exposed to various light sources and durations. Our ambient lighting is provided by ceiling fixtures, each equipped with a single orange light-emitted diode (LED). In addition, our task-oriented lighting, mounted below each wall-mounted cabinet and inside the fume hoods, is equipped with a dimmable orange LED stripline. The ambient lighting, delivering 0.4 lx at the sample position, induced a loss of less than 5 % (on average) in the quartz OSL dose after 24 h of exposure and up to 5 % (on average) in the IR50 dose for the K-rich feldspar samples, with no measurable effect on their pIR-IR290 dose. The fume hood lighting, delivering 1.1 lx at the sample position, induced a dose loss of less than 5 % in quartz OSL and K-rich feldspar IR50 doses after 24 h of exposure, with no measurable effect on their pIR-IR290 dose. As light exposure during sample preparation is usually less than 24 h, we conclude that our lighting setting is suitable for luminescence dating darkrooms; it is simple, inexpensive to build, and durable.

Feldspar traces mineralization processes in the Qongjiagang giant lithium ore district, Himalaya, Tibet

Recently, a large spodumene pegmatite deposit was discovered in the Higher Himalayan orogenic zone near Qongjiagang. The granites exposed on about 1500 vertical meters of the outcrop (with elevation varying from 4077 m to 5533 m) show an evolution from two-mica granite to tourmaline muscovite granite and tourmaline albite granite. Various types of pegmatites are dispersed throughout the granite, creating an opportunity to examine the evolutionary relationship between these rock types and their potential as ore deposits rich in lithium. This study collected feldspar samples from various granites and pegmatites along a vertical cross-section, and analyzed their structures using various techniques including Raman spectroscopy, and transmission electron microscopy. Elemental and isotopic compositions were determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometry, providing valuable mineralogical information on the formation of widespread lithium deposits in the Qongjiagang area. The observed variations in feldspar composition suggest that changes in granite lithology and ore-bearing potential of pegmatites with increasing altitude result from upward fractional crystallization of magma formed by partial melting of Himalayan crystalline basement. This process is likely driven by decreasing temperature, resulting in a significant decrease in concentrations of alkaline earth metals (e.g., Ca, Sr, Ba), and gradual enrichment of trace elements including Rb, Cs, and Li. As a result, pegmatites attain a melt environment similar to that of the adjacent granite at similar elevations. Structural features of feldspar suggest that the decrease in Li concentration in K-feldspar and the formation of lithium-rich zonation of pegmatites are a result of simultaneous growth of spodumene and blocky orthoclase during the magmatic stage, as well as deuteric fluid extraction by syntectonic processes during the transition to the stable stage of microcline feldspar.

The microstructural representation and fractal nature intepolation analysis of feldspar

This paper presents a comparative analysis of microstructural parameters by the powder X-ray diffraction method on a polycrystalline sample and the fractal analysis. The presented results of microstructural parameters are obtained by crystallographic programs FullProf based on the Rietveld method. The synthetic Ba/Ca-celsian sample has been used for microstructural parameters analysis. The feldspar sample has been synthesized by the thermal induction phase transformation process of ion exchange Ca-LTA zeolite with Ba cation. After the ion exchange Ba/Ca-LTA, the sample was heated at the temperature of 1300?C and the structure of Ba/Ca-feldspar was determined by the X-ray powder diffraction analysis. The X and U shape parameters that contribute to the strain have been reconstructed by fractal interpolation. Once we can reconstruct the shapes, which are quantum mechanics effects, we should provide the data for predicting desired parameters mentioned previously. We reported in this paper the successful application of this advanced and deep microstructure analysis, which confirmed original fractal copies based on the presented morphology characterization.

Thermodynamic mechanism and its geological significance in the transformation of albite under inorganic acid environments based on the total dissolution model

Feldspar of lithosphere undergoes transformation in an acidic fluid environment. This process significantly influences the transformation of sandstone reservoirs in sedimentary basins. Currently, there is debate on the transformation mechanism, which has led to debates in predictions of favorable reservoirs in deep sedimentary basins, in terms of their origin, type, and distribution. In this study, the transformation process of feldspar is determined based on the total dissolution model, and thermodynamics is used in the calculation process. Firstly, the precipitation order of the minerals and the reaction path during the transformation process are determined. Secondly, the obtained results are compared with the results of weathered feldspar samples, laboratory-based physical simulation samples, and sandstone samples from a sedimentary basin. Finally, the changes of sandstone reservoirs which is caused by feldspar transformation processes are discussed. Based on those results, it can be deduced that the release of inter-granular particles (Na/K/Ca) in feldspar does not conform to the total dissolution model, whereas the release of lattice particles (Si and Al) conforms to the model. The total dissolution model can deduce the genetic mechanism and occurrence of authigenic kaolinite in sandstone reservoirs. When the temperature is below 120 °C, authigenic kaolinites are directly precipitated from the pore fluids or via the reaction of Al(OH)3(s) with H4SiO4(aq). The kaolinite aggregates are worm-like, with a pure chemical composition. When the temperature is above 120 °C, the feldspar particles react with Al(OH)3(s) and transformed to kaolinites. The kaolinite aggregates are particle-like, containing heteroatoms. The differences in the genetic mechanism of kaolinite lead to evident differences for type and distribution of secondary pores formed during feldspar transformation.

Does hole instability cause anomalous fading of luminescence in feldspar?

Optically or thermally stimulated luminescence (OSL or TL) from feldspar, the most ubiquitous mineral in the Earth's crust is widely used in dosimetry and geochronology. Despite decades of research, the mechanism of OSL and TL dose underestimation arising from anomalous fading in feldspars remains poorly understood. It is commonly assumed that anomalous fading arises from the tunnelling of electrons from the principal trap, however, this causal mechanism has never been confirmed because of the lack of methods available to directly probe the trapped electrons. The recent discovery of infrared photoluminescence (IRPL), a radiophotoluminescence (RPL) signal produced by intra-defect resonant excitation in the electron trap, allows direct testing of this assumption. The unique coupled RPL-OSL physical system available in feldspar can provide insights into the dynamics of both electron and hole traps individually and, thus, improve our understanding of electron-hole recombination in this complex material.Here we use the differential IRPL signal (ΔIRPL), a quantity proportional to the number of electrons leaving the principal trap upon optical excitation, to directly measure the OSL recombination efficiency (luminescence emission per detrapped electron) for the first time. Our investigations on nine potassium(K)-rich natural feldspar samples, extracted from known-age sediments, suggest that there exist at least two competitive recombination pathways for a detrapped electron: one that produces Infrared Stimulated Luminescence (IRSL or IR-OSL) by electron-hole recombination at the blue-emission centre, and the other that leads to either luminescence quenching or emission in a different wavelength region. Contrary to the widely accepted anomalous-fading model, our results demonstrate that anomalous fading originates primarily from a change in the recombination efficiency, likely due to the athermal loss of holes at the IRSL (blue) recombination centre. A direct loss of electrons in the principal trap is relatively minor compared to the change in the recombination efficiency. Importantly, our new approach allows us to decouple the individual losses in the electron and hole traps and provide the very first direct insights into the fate of the electrons when they leave the trap.

Photoconductivity on K-feldspar

In the development of most phenomenological models used to explain the infrared excited luminescence, a major assumption is usually made in the degree of freedom the excited charge has. One of the two extremes is normally assumed: charge is free to move anywhere over the whole crystal, or it is confined close to the trap and the centers immediately adjacent to it. Determining which of these extremes is more reasonable is difficult to do on the basis of the temporal behavior of the luminescence intensity alone. However, this assumption has important consequences for the understanding of the dynamics of the luminescence process because of the difference in the number of recombination and trapping centers available to the excited charge. Additional experimental evidence was thus sought on this aspect of charge movement. One such experiment is the detection of photoconductivity in which an electrical current is measured during optical excitation or shortly there-after. In this paper, the details of photoconductivity experiments on K crystal are presented. Photoconductivity measurements were inconclusive as to whether or not there was a current flowing during the 850 nm excitation of a feldspar sample. However, there was a clear current when exciting the same sample with 515 nm light, but there was a complex relationship between the magnitude of the current and the number of emission photons counted. A model was developed to explain the photoconductivity results where electrons migrate through the conduction band aided by thermal excitation and tunneling.

Using Infra-red stimulated luminescence and phototransferred thermoluminescence to investigate electron trapping and charge transport in feldspars

Previous studies have observed mineral specific variations in the ratios of IRSL signals stimulated at the different discrete wavelengths of lines corresponding to Xe lamp emission lines, which fall within the broad excitation spectrum of IRSL. Meanwhile recent accounts of IRSL have referred to single trapping systems within the excitation band, and modelled excitation spectra as continuous gaussian distributions. A simple single trap model should not result in variations in the ratio of IRSL intensities produced at different wavelengths. In the study reported here 22 different feldspar samples, which have all been characterised by SEM and x-ray analysis, were measured using a portable OSL instrument equipped with 890 nm and 940 nm diode arrays to confirm and extend the previous observations of variations in IRSL intensity ratios. Of the samples investigated the sensitivity varied over 3–4 orders of magnitude. Albite samples in this selection showed consistently high responses. The plagioclase samples show significant variations, and the microcline and K-feldspar samples produced a large range of responses. Excitation ratios of 940 nm–890 nm show mineralogically linked variations which together with the earlier Xe lamp data point to distributions of trapping systems within the variable environments of these minerals. These results do not readily fit simple single trap models for luminescence from feldspars; instead, they suggest multiple traps or a series of similar traps which are significantly perturbed by their local lattice structural environments. Post Stimulation Phosphorescence (PSP) was observed for all samples, and phototransferred thermoluminescence (PTTL) has also been confirmed following IR stimulation suggesting that recombination mechanisms involve charge mobility and interactions with shallow traps in band-tail states rather than primarily being associated with direct quantum tunnelling recombination. The relative proportions of PSP to prior IRSL also varied between the two stimulation wavelengths which further emphasises the physical differentiation between processes influencing different subpopulations of the trapping states associated with IRSL and their local lattice environments.

불소 오염토양의 기원별 오염특성을 파악하기 위한 광물학적 특성분석 및 세척효율평가

In this study, mineralogical characteristics analysis and extraction characteristics evaluation were performed to identify the contamination characteristics by origin of fluoride-contaminated samples of natural origin by granite mica and artificial fluoride-contaminated samples by waste gypsum fluoride of making fertilizer process. In samples of natural origin, mica, quartz, feldspar, fluorite, and amphibole showed the high mineral content in the order. Among them, mica, which is expected to be the causative mineral of fluorine contamination, consisted of muscovite, biotite, and lithium mica. In artificial fluoride-contaminated samples, quartz, plagioclase, illite, gypsum, sulfur, and wollastonite showed the highest mineral content in the order. Compared to the total mica content and fluorine concentration of the natural origin contaminated sample, a proportional linear relationship(R2=0.68) was shown, and this result is estimated to be the influence of natural origin by minerals in badlock not artificial contamination. When compared with the gypsum content and fluorine concentration of the artificially contaminated samples, a proportional linear relationship(R2=0.79) was shown, and the fluoride concentration was found to exceed the standard in all samples with a gypsum content of about 20 % or more. As a result of the washing efficiency test for each mica fluoride-contaminated sample, it was confirmed that the washing efficiency was relatively low with all washing agents less than 10 %, and hydrochloric acid(HCl) had the highest washing efficiency. In addition, the optimal hydrochloric acid(HCl) concentration was confirmed to be 1 M. As a result of the washing efficiency test for each washing agent for the fluorine-contaminated sample of a fertilizer factory, sodium hydroxide(NaOH) was confirmed to have the highest washing efficiency and showed about 1.5 times higher than hydrochloric acid(HCl). In addition, the optimal concentration of sodium hydroxide(NaOH) is judged to be suitable at 0.5 M, which showed a washing efficiency of 65.6 %. Based on the results of this study, it is intended to be used as a basic data for the development of soil remediation technology considering the method of proving the cause of fluoride-contaminated soil and the characteristics of contamination by origin.

Investigating the applicability of a standardised growth curve approach on Middle Pleistocene sediments from northern Switzerland

The introduction of the Single Aliquot Regenerative Dose (SAR) protocol established luminescence dating as an indispensable tool in Quaternary research. A major impediment of this technique is the time required for measurements, since the protocol is repeated for various aliquots of each sample to establish a sound statistical basis. To reduce the demand on machine time, Standardised Growth Curve (SGC) approaches have been developed and successfully applied for samples from some regions. However, differences in luminescence properties require careful testing of this techniques when applied to samples with other geological background. In this study, the application of the SGC approach of Li et al. (2016) is successfully verified for multi-grain aliquots of coarse-grained quartz and feldspar samples from three sites in northern Switzerland. In-depth quality control measures ensure the reproducibility of equivalent dose (D e ) values obtained by the common SAR protocol and sample-specific SGCs. For both minerals little sensitivity was found to the re-normalisation dose and the sample-specific SGCs performed well. In contrast to other studies, no different types of dose response curve shape were observed for quartz. A minimum number of full SAR measurements of eight and six aliquots per sample has been found appropriate for quartz and feldspar, respectively. For the fading corrected feldspar signals, site-specific SGC worked well and D e values of up to 800 Gy were consistently replicated. In summary, sample-specific SGCs for samples from northern Switzerland perform well and their application reduces measurement times by up to 70%. The construction of a regional SGC may well be beneficial, however, caution regarding the choice of given doses and curve fitting is recommended and a thorough verification of SGC results is needed before the technique is widely applied. • Application of the standardised growth curve approach (SGC). • Sample- and site-specific SGCs successful for feldspar and quartz. • Application of a regional SGC for fading corrected feldspar signals with caution.

Factors affecting bioleaching in the processing of non-metallics

Biotechnological treatment of non-metallics is based on bacterial leaching of raw material and dissolution of Fe. Bacterial iron dissolution ability is dependent on various physicochemical factors as temperature, acidity of solutions, redox potential, rapidity of water circulation and presence of organic sources. The Fe content in the quartz sands and feldspar samples by the biological leaching decreased as much as 60% and by subsequent using of electromagnetic separation of feldspars, the decrease of Fe content in 74% was achieved. However, the application of magnetic separation of quartz sands after bioleaching resulted in total iron removal of 93% and in such combined way prepared product contained 0.024 % of Fe2O3. Achieved results on iron removal point to the fact that combination of leaching and magnetic separation enables to obtain product usable in glass and ceramic industry.

Optically stimulated luminescence dating supports pre-Eemian age for glacial ice on the Lomonosov Ridge off the East Siberian continental shelf

Establishing a solid chronological framework for Arctic marine sediments is a critical first step towards glacial and palaeoceanographic reconstructions. However, this has historically been more challenging than elsewhere in the world, and often results in core chronologies and subsequent paleoenvironmental reconstructions being questioned and overturned. Optically stimulated luminescence (OSL) dating provided important constraints on late Quaternary ages for central Arctic marine sediments, and has considerable potential to underpin chronologies in other parts of the Arctic Ocean. This study applies OSL and infrared stimulated luminescence (IRSL) geochronology to multi-grain quartz and feldspar samples from a sediment core collected from the Lomonosov Ridge off the Siberian shelf during the 2014 SWERUS-C3 Expedition. Testing and advancing the proposed chronology of late Quaternary sediments in this part of the Arctic is essential to better constrain the timing of ice sheet growth on the Siberian Arctic shelf and subsequent ice shelf development in the Arctic Ocean. The results of luminescence dating support a pre-Eemian age for extensive ice grounding and scouring of the southern Lomonosov Ridge. Furthermore, we combine the OSL ages with data from rock magnetic measurements and propose an age-depth model for cores in this region. As in other areas in the Arctic, magnetic grain size/mineralogy profiles resemble the global oxygen isotope curve and may have the potential to be a dating tool. This can be tested and further refined in future studies that obtain longer sedimentary archives. Our results also indicate that changes in the inclination of the natural remanent magnetisation do not reflect geomagnetic field variation in the investigated sediment cores.

Mid-infrared spectroscopy of crystalline plagioclase feldspar samples with various Al,Si order and implications for remote sensing of Mercury and other terrestrial Solar System objects

We analyzed plagioclase feldspar samples that were well-characterized in terms of chemical composition as well as degree of Al,Si order in mid-infrared reflection spectra between 7 μm and 14 μm (1429 cm−1 and 714 cm−1). The chemical compositions were derived with an electron microprobe analyzer. To determine the degree of Al,Si order, powder X-ray diffraction methods were applied. For the interpretation of the infrared spectra, we used the wavelength of the Christiansen feature (CF) and the autocorrelation function for a specific wavelength region. The CF shifts from around 7.72 μm (1296 cm−1) in Na-richest samples to 8.10 μm (1234 cm−1) in the Ca-richest sample. Combining the CF position and the autocorrelation-derived value allowed to determine the degree of Al,Si order of the samples based on reflection spectra. The wavelength of the Transparency feature (TF) in the finest analyzed grain size fraction also depends on the chemical composition and the degree of Al,Si order. Our results are helpful for the interpretation of data returned by the MERTIS experiment onboard BepiColombo. The data help to distinguish between space weathering, shock effects, and ordering effects in plagioclase samples.

Compositional characteristics and Ta-Sn-Nb rare metal mineralization potential of Egbe Pegmatite, Southwestern Nigeria

Pan African (600 ± 150) pegmatite which intrudes gneisses, amphibolites, quartzite and schists around Egbe area were studied for their compositional features. This is with a view to characterizing and assessing their potential for rare metal Ta-Sn-Nb mineralization. Twenty seven samples comprising eleven (11) whole rock, sixteen (12) muscovite extracts and four (4) feldspar extracts samples were analyzed using the Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Major oxide geochemical assessment of the whole rock pegmatite indicates that the pegmatite is siliceous (79.82% SiO2) and moderately high in Al2O3 (12.22%). The K2O, Na2O contents are averagely 2.25% and 2.87% respectively while Fe2O3, MnO, MgO are each less than 1.0%.&#x0D; Average values of trace elements in the pegmatite are Ta (52.55ppm), Sn (92.3 ppm), Rb (1083.5ppm), Nb (109.35 ppm), Cs (32.12ppm), Sr (17.84 ppm), Y (9.86 ppm), and Zr (41.27 ppm), Ba (50.47ppm), Hf (12.38ppm), Zr (41.27ppm), Ga (32.12ppm) and W(2.91PPM) and ratios of diagnostic elements are K/Rb (30.27), Rb/Sr (298.93), Zr/Hf (7.23), Rb/Cs (65.80), K/Cs (1103.11), Ta/W (41.81), Nb/Ta (55.397) Na/Rb (41.77) and Na/K (92.25) A/CAN &gt;1and Al2O3&gt;CaO+ Na2O+ K2O with enrichment of SiO2, Al2O3, Na2O, K2O and depletion of Fe2O3, MnO2 and MgO suggests that Egbe pegmatite is of peraluminous bulk composition and plots of A/NK vs Al/CNK and Rb vs (Y+Nb) discriminates Egbe pegmatite in the peraluminous LCT (Li, Rb, Cs, Be, Ga, Nb &lt;,&gt; Ta, Sn, Hf, B, P, F) of syncollisional to within plate granitic family. The Ta/W vs Cs plot for the three sample media shows the relationship between increasing Ta/W ratio and elemental fractionation as indicated by Cs. The K/Rb vs Cs and K/Rb vs Rb plots for the three sample media further establishes the rare – metal nature and mineralization potential of Egbe pegmatite. Using the discriminant plots of TaVs Rb, Ta vs Cs .TaVs K/Cs, and Ta Vs (Cs+Rb) where most of the samples of the whole rock pegmatite and mineral extracts plots above the Beus line and about 30% plotting above the Gordinyenko line respectively. Overall geochemical assessment is that Egbe pegmatite is a rare metal, highly fractionated Beryl type with rare metal enrichment trend of Nb&gt;&gt;Sn&gt;&gt;Ta.&#x0D; Keywords: Pegmatite, Peraluminous, Syncollisional, Within-plate, Discriminant, Fractionation, Sample media

Mid-infrared spectroscopy of alkali feldspar samples for space application

Feldspars are major components of terrestrial planetary surfaces. For future space application and the setup of a comprehensive reference database, Na- and K-rich alkali feldspars, NaAlSi3O8 – KAlSi3O8, have been investigated by infrared reflectance spectroscopy. We related the feldspar spectra to the chemical composition and state of Al,Si order/disorder. The infrared measurements were analyzed with respect to band shifts and peak shapes using the autocorrelation function. Natural samples served as starting materials. Some samples were treated by the alkali exchange method to produce pure end-members, which were then heated to generate various states of Al,Si disorder. X-ray diffraction (XRD) methods served to determine the Al,Si distribution. Our autocorrelation allowed to differentiate between the compositional and the order/disorder influences seen in the spectra in the wavelength range between 7 μm up to 14 μm (1429 cm− 1 to 714 cm− 1). Space missions often analyze the surfaces of planetary bodies using remote sensing. Therefore, our results are essential to characterize and distinguish alkali feldspars on the surfaces of terrestrial planetary bodies like Mercury.

X-ray Fluorescence Analysis of Feldspars and Silicate Glass: Effects of Melting Time on Fused Bead Consistency and Volatilisation

Reproducible preparation of lithium tetraborate fused beads for XRF analysis of glass and mineral samples is of paramount importance for analytical repeatability. However, as with all glass melting processes, losses due to volatilisation must be taken into account and their effects are not negligible. Here the effects of fused bead melting time have been studied for four Certified Reference Materials (CRM’s: three feldspars, one silicate glass), in terms of their effects on analytical variability and volatilisation losses arising from fused bead preparation. At melting temperatures of 1065 °C, and for feldspar samples, fused bead melting times shorter than approximately 25 min generally gave rise to a greater deviation of the XRF-analysed composition from the certified composition. This variation might be due to incomplete fusion and/or fused bead inhomogeneity but further research is needed. In contrast, the shortest fused bead melting time for the silicate glass CRM gave an XRF-analysed composition closer to the certified values than longer melting times. This may suggest a faster rate of glass-in-glass dissolution and homogenization during fused bead preparation. For all samples, longer melting times gave rise to greater volatilisation losses (including sulphates and halides) during fusion. This was demonstrated by a linear relationship between SO3 mass loss and time1/2, as predicted by a simple diffusion-based model. Iodine volatilisation displays a more complex relationship, suggestive of diffusion plus additional mechanisms. This conclusion may have implications for vitrification of iodine-bearing radioactive wastes. Our research demonstrates that the nature of the sample material impacts on the most appropriate fusion times. For feldspars no less than ~25 min and no more than ~60 min of fusion at 1065 °C, using Li2B4O7 as the fusion medium and in the context of feldspar samples and the automatic fusion equipment used here, strikes an acceptable (albeit non-ideal) balance between the competing factors of fused bead quality, analytical consistency and mitigating volatilisation losses. Conversely, for the silicate glass sample, shorter fusion times of less than ~30 min under the same conditions provided more accurate analyses whilst limiting volatile losses.

Corrigendum to "ATR-FTIR and XRD quantification of solid mixtures using the asymptotic constant ratio (ACR) methods. Application to geological samples of sodium and potassium feldspars" [Spectrochim. Acta A 236 (2020) 118328

Corrigendum to "ATR-FTIR and XRD quantification of solid mixtures using the asymptotic constant ratio (ACR) methods. Application to geological samples of sodium and potassium feldspars" [Spectrochim. Acta A 236 (2020) 118328