This work focuses on a characterization of various type of luminescence in Moganite‐rich silica minerals from Mogan (Gran Canaria, Spain). The silica minerals formed by complicated hydrous processes exhibit luminescence emissions, which depend on sample temperature and type of an irradiation for excitation such as heat, laser, ion‐beam, X‐ray, incident electron beam and so on. Here we examined thermoluminescence (TL), ion beam luminescence (IBL), radioluminescence (RL), cathodoluminescence (CL) of moganite aliquots combined with Raman spectroscopy for clarification of relationship between lattice defects and the spectral luminescence emissions. The spatially‐resolved CL spectroscopy coupled to the environmental scanning electron microscopy (ESEM‐CL) displays different luminescence spectral signals between the moganite veined core (dull emission) and the rim (bright emission) together with larger porosity and additional ions in the outer part, suggesting a later alteration process with alkali, metals and volatile ions for the moganite formation. RL and IBL spectra of silica minerals in core and rim mainly show a progressive increase in intensity of RL emission band at 470–500 nm with decrease in sample temperature, which is caused by cryogenic stress on the [AlO4]0 centers. Continuous H+ ion beam implantation on samples at room temperature produces a subtle diminishing of blue emission and a quite brightening of red emission at 700 nm assigned to Fe3+ point defects. The white turbid rim with opaline SiO2 in cavities emits bright CL emission in panchromatic CL image, and has spectral emission bands at 290 nm with high intensity (100 000 a.u.) and one at 520 nm which are probably related to H2O(Si‐OH) groups, H+, Na+ and metallic ions such as Fe3+, Ti4+ and Nb4+. Moganite core zones only display emission bands at 390 nm and 670 nm (8500 a.u.) attributed to [AlO4/Na+]0 centers and silanol groups, respectively.
The interaction of linearly polarised ultrashort laser pulses with optically active devices such as half- or multi-order wave plates is considered. It is shown that, for pulses having coherence lengths comparable to their centre wavelength, such devices do not act in the usual manner and a method of measuring the duration of the pulses is proposed. It is pointed out that radiation of sufficiently broad bandwidth is capable of exhibiting a polarisation state not possible for quasi-monochromatic radiation.
Coral skeletal B/Ca (effectively B/CO32–), in combination with boron isotopic composition (δ11B), has been used to reconstruct the dissolved inorganic carbon chemistry of coral calcification media and to explore the biomineralisation process and its response to ocean acidification. This approach assumes that B(OH)4−, the B species incorporated into aragonite, competes with dissolved inorganic carbon species for inclusion in the mineral lattice. In this study we precipitated aragonite from seawater in vitro under conditions that simulate the compositions of the calcification media used to build tropical coral skeletons. To deconvolve the effects of pH and [CO32–] on boron incorporation we conducted multiple experiments at constant [CO32–] but variable pH and at constant pH but variable [CO32–], both in the absence and presence of common coral skeletal amino acids. Large changes in solution [CO32–], from < 400 to >1000 µmol kg−1, or in precipitation rate, have no significant effect on aragonite B/Ca at pHtotal of 8.20 and 8.41. A significant inverse relationship is observed between solution [CO32–] and aragonite B/Ca at pHtotal = 8.59. Aragonite B/Ca is positively correlated with seawater pH across precipitations conducted at multiple pH but this relationship is driven by the effect of pH on the abundance of B(OH)4– in seawater. Glutamic acid and glycine enhance the incorporation of B in aragonite but aspartic acid has no measurable effect. Normalising aragonite B/Ca to solution [B(OH)4–] creates KDB(OH)4− which do not vary significantly between pH treatments. This implies that B(OH)4– and CO32– do not compete with each other for inclusion in the aragonite lattice at pHtotal 8.20 and 8.41. Only at high pH (8.59), when [B(OH)4–] is high, do we observe evidence to suggest that the 2 anions compete to be incorporated into the lattice. These high pH conditions represent the uppermost limits reliably measured in the calcification media of tropical corals cultured under present day conditions, suggesting that skeletal B/Ca may not reflect the calcification media dissolved inorganic carbon chemistry in all modern day corals.
Abstract The magmatic-hydrothermal transition in granite-related, rare-metal metallogenic systems has received great attention as economic rare metal (including rare earth) minerals reach saturation and trigger mineralization at this stage. However, deciphering the details of the melt-fluid evolution process and the distribution behavior of rare metals remains difficult. Here, we applied tourmaline chemistry and B isotopes to unravel processes at the magmatic-hydrothermal transition that are responsible for rare-metal partitioning in the Huoshibulake (HS) and Tamu (TM) REE-Nb-mineralized intrusions in Southern Tianshan, SW Central Asian Orogenic Belt. Three types of tourmaline are identified in the plutons: (1) disseminated tourmaline in the granite, with a brown-yellow core (HS-DB) and blue-green rim (HS-DG); (2) orbicular tourmaline, with a brown-yellow core (HS-OB and TM-OB) and blue-green rim (HS-OG and TM-OG); and (3) vein tourmaline (HS-V and TM-V). Compositionally, all these tourmalines exhibit extremely low Ca and Mg contents and are classified as schorl. The substitution processes of major-element variations are dominantly caused by (Al,☐)(Fe,Na)−1 exchange vectors. Four generations of tourmaline crystallization are established based on the petrographic, compositional, and B isotopes evolution of the tourmaline. First, the HS-DB crystals crystallized from the highly evolved residual melt, and then HS-OB and TM-OB precipitated from immiscible B-rich aqueous melts during the magmatic-hydrothermal transition. Subsequently, the blue-green overgrowths (HS-DG, HS-OG, and TM-OG) crystallized from exsolved hydrothermal fluids. Finally, the formation of HS-V and TM-V resulted from another melt pulse from a deeper magma chamber. The magmatic tourmaline exhibits a narrow range of δ11B values between –12.6 to –10.0‰, while the hydrothermal tourmaline shows significantly heavier and variable δ11B values ranging from –10.2 to –4.9‰. The fractionation of B isotopes is reproduced by Rayleigh fractionation modeling. Lower Nb and Sn contents in the orbicular tourmaline relative to those precipitated from the residual melt, along with the lack of rare-metal minerals in the orbicules, indicate that B-rich melt/fluid exsolution does not necessarily contribute to the rare-metal mineralization. In comparison, the veins contain abundant rare-metal and REE minerals in close paragenesis with fluorite, and the vein tourmaline shows high-Nb and -Sn contents. These observations suggest that saturation of fluorite triggered the precipitation of rare metals, and fluorine played a critical role in rare metal concentration and mineralization. This study highlights the potential of tourmaline to trace the magmatic-hydrothermal transition and provide insights into rare-metal mineralization in the granitic systems.
Structural analysis, using neutron powder diffraction (NPD) data on small quantities (<300 mg) and in combination with single-crystal X-ray diffraction (SXD) data, has been employed to determine accurately the position of hydrogen and other light atoms in three rare beryllate minerals, namely bavenite, leifite/IMA 2007-017, and nabesite. For bavenite, leifite/IMA 2007-017, and nabesite, significant differences in the distribution of H, as compared to the literature using SXD analysis alone, have been found. The benefits of NPD data, even with small quantities of H-containing materials, and, more generally, in applying a combined SXD-NPD method to structure analysis of minerals are discussed, with reference to the quality of the crystallographic information obtained.
The optically stimulated luminescence (OSL) signals of quartz and K-feldspar are known to bleach poorly within some glacial settings, and can present a major challenge to dating applications. However, because the OSL signal is extremely sensitive to sunlight exposure history, the residual luminescence signals of modern glacial sediments also encode information about transport and depositional processes. Through examination of the residual luminescence properties (equivalent dose (De) and overdispersion values) of a suite of modern glacial sediments from different depositional settings (sandar, proglacial delta and main meltwater channel), this study provides insights not only into which sediments are likely to be fully bleached within glacial settings, but also into how OSL can be used to trace different depositional processes across sedimentary landforms. Improved understanding of the processes of sediment bleaching will enable better sample selection and may improve the accuracy and precision of OSL dating of glacial sediments. The luminescence signals of both coarse-grained quartz and K-feldspar with similar sediment sources are found to be sensitive to both depositional process and specific depositional setting. Whereas modern braid-bar-head deposits from the Nigardsdalen ice-proximal proglacial delta typically have ages of ≤3 ka, similar depositional features from the Fåbergstølsgrandane sandur have residual ages of ≥26 ka. Exploration of changing residual luminescence signals across individual sandur and proglacial delta braid-bar features shows that braid-bar-head deposits can retain large residual De values, while the partner braid-bar-tail deposits are almost completely bleached. The quartz OSL signal and K-feldspar IRSL50 and post-IR IRSL250 signals are shown to bleach at the same rate across the same bar feature and the IRSL50 K-feldspar signal is also shown to be completely bleached for bar-tail deposits in Nigardsdalen. Therefore the IRSL50 K-feldspar signal is suitable for dating some glacial deposits, circumventing the challenges associated with dim quartz signals.
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