Structural and thermodynamic properties of Ca-Al-bearing amphiboles

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The α–β phase transition in volcanic cristobalite

Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the cristobalite it contains. Volcanic cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic cristobalite are known to modify the crystal structure, affecting the stability of the [alpha] and [beta] forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the [alpha]-[beta] phase transition in volcanic cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic cristobalite exists in the [alpha] form and has a larger cell volume than synthetic [alpha]-cristobalite; as a result, its diffraction pattern sits between ICDD [alpha]- and [beta]-cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic cristobalite exhibits a lower degree of thermal expansion than synthetic cristobalite, and it also has a lower [alpha]-[beta] transition temperature (~473 K) compared with synthetic cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al3+ and Na+ defects. The transition shows a stable and reproducible hysteresis loop with [alpha] and [beta] phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures

Novel multi-isotope tracer approach to test ZnO nanoparticle and soluble Zn bioavailability in joint soil exposures

Here we use two enriched stable isotopes, 68Znen and 64Znen (>99%), to prepare 68ZnO nanoparticles (NPs) and soluble 64ZnCl2. The standard LUFA 2.2 test soil was dosed with 68ZnO NPs and soluble 64ZnCl2 to 5 mg kg–1 each, plus between 0 and 95 mg kg–1 of soluble ZnCl2 with a natural isotope composition. After 0, 1, 3, 6, and 12 months of soil incubation, earthworms (Eisenia andrei) were introduced for 72 h exposures. Analyses of soils, pore waters, and earthworm tissues using multiple collector inductively coupled plasma mass spectrometry allowed the simultaneous measurement of the diagnostic 68Zn/66Zn, 64Zn/66Zn, and 68Zn/64Zn ratios, from which the three different isotopic forms of Zn were quantified. Eisenia andrei was able to regulate Zn body concentrations with no difference observed between the different total dosing concentrations. The accumulation of labeled Zn by the earthworms showed a direct relationship with the proportion of labeled to total Zn in the pore water, which increased with longer soil incubation times and decreasing soil pH. The 68Znen/64Znen ratios determined for earthworms (1.09 ± 0.04), soils (1.09 ± 0.02), and pore waters (1.08 ± 0.02) indicate indistinguishable environmental distribution and uptake of the Zn forms, most likely due to rapid dissolution of the ZnO NPs

Skeletal carbonate mineralogy of Scottish bryozoans

This paper describes the skeletal carbonate mineralogy of 156 bryozoan species collected from Scotland (sourced both from museum collections and from waters around Scotland) and collated from literature. This collection represents 79% of the species which inhabit Scottish waters and is a greater number and proportion of extant species than any previous regional study. The study is also of significance globally where the data augment the growing database of mineralogical analyses and offers first analyses for 26 genera and four families. Specimens were collated through a combination of field sampling and existing collections and were analysed by X-ray diffraction (XRD) and micro-XRD to determine wt% MgCO3 in calcite and wt% aragonite. Species distribution data and phylogenetic organisation were applied to understand distributional, taxonomic and phylo-mineralogical patterns. Analysis of the skeletal composition of Scottish bryozoans shows that the group is statistically different from neighbouring Arctic fauna but features a range of mineralogy comparable to other temperate regions. As has been previously reported, cyclostomes feature low Mg in calcite and very little aragonite, whereas cheilostomes show much more variability, including bimineralic species. Scotland is a highly variable region, open to biological and environmental influx from all directions, and bryozoans exhibit this in the wide range of within-species mineralogical variability they present. This plasticity in skeletal composition may be driven by a combination of environmentally-induced phenotypic variation, or physiological factors. A flexible response to environment, as manifested in a wide range of skeletal mineralogy within a species, may be one characteristic of successful invasive bryozoans

Up-Cycling Waste Glass to Minimal Water Adsorption/Absorption Lightweight Aggregate by Rapid Low Temperature Sintering: Optimization by Dual Process-Mixture Response Surface Methodology

Mixed color waste glass extracted from municipal solid waste is either not recycled, in which case it is an environmental and financial liability, or it is used in relatively low value applications such as normal weight aggregate. Here, we report on converting it into a novel glass-ceramic lightweight aggregate (LWA), potentially suitable for high added value applications in structural concrete (upcycling). The artificial LWA particles were formed by rapidly sintering (<10 min) waste glass powder with clay mixes using sodium silicate as binder and borate salt as flux. Composition and processing were optimized using response surface methodology (RSM) modeling, and specifically (i) a combined process-mixture dual RSM, and (ii) multiobjective optimization functions. The optimization considered raw materials and energy costs. Mineralogical and physical transformations occur during sintering and a cellular vesicular glass-ceramic composite microstructure is formed, with strong correlations existing between bloating/shrinkage during sintering, density and water adsorption/absorption. The diametrical expansion could be effectively modeled via the RSM and controlled to meet a wide range of specifications; here we optimized for LWA structural concrete. The optimally designed LWA is sintered in comparatively low temperatures (825-835 °C), thus potentially saving costs and lowering emissions; it had exceptionally low water adsorption/absorption (6.1-7.2% w/wd; optimization target: 1.5-7.5% w/wd); while remaining substantially lightweight (density: 1.24-1.28 g.cm-3; target: 0.9-1.3 g.cm-3). This is a considerable advancement for designing effective environmentally friendly lightweight concrete constructions, and boosting resource efficiency of waste glass flows

Strukturelle und thermodynamische Eigenschaften von Ca-Al-haltigen Amphibolen

In dieser Arbeit wurden die Ca-Sr-Substitution und die Mg-Tschermaks Substitution (MgSi = AlAl) in dem Amphibol Tremolit sowie die Ca-Sr-Substitution in dem Pyroxen Diopsid experimentell untersucht. Die Amphibol- und Pyroxensynthesen wurden in Anwesenheit einer halogenidischen Lösung durchgeführt. Die Experimente zur Ca-Sr Substitution erfolgten bei 750°C und 200 MPa und die Experimente zur Mg-Tschermaks-Substitution bei 600-850°C und 200-2000 MPa. Sowohl Tremolit- als auch Diopsidstruktur erwiesen sich als flexibel für den vollständigen Ersatz des Ca durch Sr. Zwischen Tremolit und Sr-Tremolit existiert eine kontinuierliche Mischkristallreihe. (Ca,Sr)-Diopside konnten in den Bereichen von XSr = 0.00-0.31 und 0.90-1.00 synthetisiert werden. Mischkristalle entlang des Mg-Tschermaksvektors konnten zwischen Tremolit und Magnesiohornblende beobachtet werden. Die Gitterkonstanten von Tremolit und Diopsid verändern sich mit zunehmenden Sr-Einbau linear. Zunehmender Sr-Einbau führt zur Zunahme der Zellparameter a, b und ß im Tremolit sowie a und b im Diopsid, wobei sich ß im Diopsid verringert. Eine lineare Änderung konnte auch mit zunehmender Mg-Tschermakskomponente im Tremolit verzeichnet werden, wobei die Zellparameter a und b abnehmen und c und ß zunehmen. IR-Untersuchungen zeigten, daß der Einbau von Sr und Al im Tremolit eine komplexe Feinstruktur der OH-Streckschwingungsbande bewirkt. Die Feinstruktur konnte hierbei im (Ca,Sr)-Tremolit der Substitution von Sr, Ca, und Mg auf der M4-Position zugeordnet werden. Im Al-Tremolit wird die Feinstruktur durch Mg-Al-Substitution auf M2- und M3-Positionen sowie Si-Al-Substitution auf T1-Positionen verursacht. Quantitative Berechnungen zu den Bandenzuordnungen deuten hierbei auf eine statistische Verteilung von Sr, Ca, und Mg auf der M4-Position sowie von Mg und Al auf M2- und M3-Positionen im Tremolit hin. Das Verteilungsverhalten von Sr und Ca zwischen Tremolit, Diopsid und chloridischer Lösung wurde bei 750°C und 200 MPa untersucht. Sr fraktioniert hierbei stark in die Fluidphase. Die Mineral/Fluid-Verteilungskoeffizienten für Sr von D(Sr, Amphibol/Fluid) = 0.045 und D(Sr, Pyroxen/Fluid) = 0.082 wurden abgeleitet. Die Mischungsenergien in (Ca,Sr)-Tremolit- und (Ca,Sr)-Diopsid-Serie wurden mit einem regulären Mischungsmodell berechnet, wobei die Wechselwirkungsparameter von W (CaSr, Amphibol) = 9.8 kJ und W (CaSr, Pyroxen) = 11.7 kJ ermittelt wurden. Verschiedene ideale Mischungsmodelle wurden für die Mg-Tschermaks-Substitution entlang der Tremolit-Tschermakit-Mischkristallreihe getestet. Der beste Fit für die thermodynamischen Daten des Tschermakit wurde mit der Verwendung des two-site coupled Modells erzielt. Für Tschermakit konnte eine Standardbildungsenthalpie von -12528.3 ± 11.7 kJ/mol und eine Standardentropie von 556.5 ± 12.0 J/K/mol extrahiert werden.The Ca-Sr and Mg-tschermaks (MgSi = AlAl) substitutions in tremolite, and the Ca-Sr substitution in diopside were experimentally investigated. Syntheses were performed in the presence of a halogenidic fluid. Experiments about Ca-Sr substitution were carried out at 750°C and 200 MPa and experiments about Mg-tschermaks substitution were carried out at 600-850°C and 200-2000 MPa. Both tremolite and diopside structures are flexible for a complete substitution of Sr for Ca. A continuous solid solution series exists between tremolite and Sr-tremolite. (Ca,Sr)-diopside solid solutions could be synthesized between XSr = 0.00-0.31 and 0.90-1.00. Along the Mg-tschermaks vector solid solutions between tremolite and magnesiohornblende were observed. The lattice parameters of tremolite and diopside are a linear function of the Sr-content. For (Ca,Sr)-tremolites the lattice parameters a, b and ß increase with increasing Sr-content. For (Ca,Sr)-diopsides a and b increase and ß decreases with rising Sr-content. Increasing Mg-tschermaks content in tremolite also changes the lattice parameters linearly, a and b decrease whereas c and ß increase. Complex fine structures of the OH stretching bands can be observed in IR spectra of (Ca,Sr)-tremolites and Al-tremolites. Fine structures were assigned to substitutions of Sr, Ca and Mg on M4 sites in (Ca,Sr)-tremolite, and to Mg-Al substitution on M2 and M3 sites and Si-Al substitution on T1 site in Al-tremolite. The assignments were supported by quantitative calculations, which indicate a statistical distribution of Sr, Ca and Mg on M4 sites and Mg and Al on M2 and M3 sites in tremolite. The distribution of Sr and Ca between tremolite, diopside and chloridic solution were investigated at 750°C and 200 MPa. Sr fractionates strongly into the fluid. The mineral/fluid partition coefficients for Sr are D(Sr amphibole/fluid) = 0.045 and D(Sr pyroxene/fluid) = 0.082. The mixing energies of (Ca,Sr)-tremolite and (Ca,Sr)-diopside series were calculated using a regular solution model. Interaction parameters of W(CaSr, amphibole) = 9.8 kJ and W(CaSr, pyroxene) = 11.7 kJ were derived. The thermodynamic properties of the tschermakite endmember and the mixing properties along the tremolite-tschermakite join were extracted from six exchange reactions. Ideal mixing models were tested for Mg-tschermaks substitution along the tremolite-tschermakite join. Best fits were obtained for a two-site coupled model, resulting in an enthalpy of formation of -12528.3 ± 11.7 kJ/mol and a standard entropy of 556.5 ± 12.0 J/mol/K for tschermakite endmember

The Unexpected Discovery of Syngenite on Margarito d’Arezzo’s <i>The Virgin and Child Enthroned, with Scenes of the Nativity and the Lives of the Saints</i> (Probably 1263–4) and Its Possible Use as a Yellow Lake Substrate

The oldest painting in the National Gallery collection, The Virgin and Child Enthroned by Margarito d’Arezzo (NG564), dated to about 1263–4, depicts the Virgin and Child in a mandorla, surrounded by scenes of the Nativity and lives of the saints, set within red and decorative black borders, against a gilded background. The materials and technique were investigated using a combination of non-invasive techniques, such as Fibre Optic Reflectance Spectroscopy (FORS) and macro X-ray fluorescence scanning (MA-XRF), and the analysis of a small number of paint samples using energy dispersive X-ray analysis in the scanning electron microscope (SEM-EDS), High-Performance Liquid Chromatography (HPLC), Attenuated Total Reflectance—Fourier transform infrared spectroscopy (ATR-FTIR) and micro X-ray Diffraction (micro-XRD). The results provided evidence for the use of a number of organic colourants, with both indigo and red lake pigments identified. The finding of an unusual compound, syngenite (K2Ca(SO4)2·H2O), is here postulated as a potential substrate for an organic yellow lake pigment. In addition, reference pigments were prepared to explore this hypothesis. Although documentary evidence confirms that yellow lakes were being produced from an early date, there is very little direct evidence for their use in 13th-century panel paintings

(Supporting Information) Collection date and location of the analysed herbarium Corallina officinalis samples of the Natural History Museum (BM)

Suporting Information 1; Herbarium Corallina officinalis samples of the Natural History Museum (BM) analysed for the present study. Where the same NHM barcodes are provided for more than one sample, multiple samples were present under the same barcode in the herbarium. (-) indicates samples were not barcoded in the NHM (BM) system