X-ray Microbeam Research Articles

Study on chemical forms of aluminum in tea leaves using micro-PIXE method

Elemental analysis of the epidermis of tea leaves was performed using the micro-beam particle-induced X-ray emission (micro-PIXE) method. The ratios of the X-ray yields of silicon (Si), potassium (K), calcium (Ca), and manganese (Mn) to that of aluminum (Al) in the cell wall of epidermal cells of tea leaves were determined. The ratio of Si to Al X-ray yields agreed within a range of 11% in the four samples measured in this study. On the other hand, the ratio of the X-ray yields of K, Ca, and Mn to Al varied from 41% to 87%. This result suggests that Al forms compounds with Si in tea leaves.

Continuous Spectrum of Morphologies and Phase Behavior across the Contact Zone from Poly(l-lactide) to Poly(d-lactide): Stereocomplex, Homocrystal, and Between.

The enantiomeric ratio is a key factor affecting the crystallization behavior and morphology of poly-l-lactide/poly-d-lactide (PLLA/PDLA) blends. Despite a number of studies on crystallization of nonequimolar PLLA/PDLA blends, a full picture of the effect of the L/D ratio is still lacking. Here, we put the two enantiomers in contact and allow interdiffusion above the melting point of the stereocomplex crystal (SC) to prepare samples with a continuously changing L/D ratio from enantiopure PLLA (ratio 0/100) to enantiopure PDLA (100/0). Using polarized optical microscopy, atomic force microscopy, and microbeam X-ray diffraction, the continuous spectrum of morphologies and phase behaviors across the contact zone is investigated. The blend morphology shows clear evidence of "poisoning by purity" of SC crystallization at all blend compositions. The low birefringence of the 50/50 SC is found to be due to the meandering of broken edge-on lamellae. Its further decrease to near zero as L/D deviates further away from 50/50 is explained by transition from radial edge-on lamellae to fully random meandering lamellae, then to mixed flat-on lamellae, and finally to submicron-sized axialites. In comparison with the smooth and straight homocrystal (HC) lamellae of pure enantiomers, the lamellae in the blends often have serrated edges caused by pinning by rejected excess enantiomer acting as an impurity during lamellar growth. A feature of the binary phase diagram is pure enantiomers acting as an impurity to the SC and counter-enantiomer acting as an impurity to homocrystallization of the enantiomers. Crystallization was found to be most suppressed at 99% enantiomeric purity, where the amount of the counter-enantiomer is insufficient for creation of SC nuclei and HC growth is inhibited by the small amount of the enantio-impurity. These and other intriguing results are less likely to be noticed without the continuous composition gradient of the contact sample.

Heterogeneity effects in micro-beam XRF scanning spectroscopy of binary powdered mixtures and lake sediments

Micro-beam X-ray fluorescence (XRF) scanning spectroscopy is very useful for analyzing heterogeneous samples from earth and environmental sciences with high spatial resolution. However, XRF intensity depends on grain size and mineralogical composition, known as the heterogeneous effect, although little quantitative evaluation has been conducted. In this study, the binary powdered mixtures of Fe2O3 in the CaCO3 or SiO2 matrix with nine grain size fractions (0.3–605 μm), four Fe2O3 concentrations (5–20 wt%), and fine-grained sedimentary cores from Lake Baikal were used for analysis, using a scanning X-ray analytical microscope (SXAM), and then evaluated by making a simple modification of the Berry–Furuta–Rhodes model. The results of binary powdered samples show that the Fe intensity decreases as the grain size increases, but if the grain size is constant, its intensity has a linear relationship with the composition of Fe2O3. The experimental data are in good agreement with theoretical curves. The theory predicts that if a phase that contains fluorescent elements has narrow ranges of concentration and grain size, the micro-beam XRF spectroscopy enables highly precise calibration from the XRF intensity to element concentration. The theoretical curves of the Lake Baikal sediment core suggest that the Fe intensity has about a 30% maximum difference in the median grain size range of 3.9–28.2 μm. This variation appears in a scatter of regression between Fe intensity and concentration, but it scarcely affected the XRF intensity variability of sediment composition.

The babble of articulatory learning networks

Articulatory learning models utilize traditional neural network approaches to model speech. However,they differ in their inclusion of an intermediary step in which the model is trained to produce sound utilizing a physical model of the human vocal tract. This style of training is theoretically able to represent the impact of the physical nature of the human vocal tract on language in a way that is more directly translatable to the physical world. This project seeks to create an articulatory learning model which is trained to recognize and repeat input sounds utilizing the University of Wisconsin’s X-Ray Microbeam Database. We attempt this utilizing an inverse model which seeks to predict the vocal tract configuration of a given speech signal, and a forward model which predicts the acoustic form produced by vocal tract configurations. Further, we analyze the performance of the model across various training lengths to investigate the comparison to child language learning that is commonly made when implementing models of this type. Should this analysis of articulatory learners be valid, we look to find commonalities in the phonetic patterning of articulatory learning neural networks and those observed in the phonetic acquisition stages of child language development.

Probing the Nano-Assembly Leading to Periodic Gratings in Poly(p-dioxanone).

This study used scanning electron microscopy via 3D dissection coupled with synchrotron radiation with microfocal beams of both small-angle X-ray scattering and wide-angle X-ray diffraction to analyze the periodic crystal aggregates of unusual poly(p-dioxanone) (PPDO) dendritic cactus-arm-like ring bands upon crystallization with a diluent poly(vinyl alcohol) (PVA) that is capable of hydrogen bonding interactions with PPDO. Three-dimensional microscopy interior dissection clearly expounds that the banded periodic architectures are packed by alternately normal-oriented flat-on crystals underneath the valley, periodically interfaced/branched with horizontal-oriented edge-on fibrils underneath the ridge. The oblique angles between the valley's flat-on crystals with the branches are ca. 25-45° (depending on gradient inclines and bending), which is also proved by the azimuthal angle in microbeam X-ray diffraction. The grating-like strut-rib assembly in the PPDO cactus-arm-like ring bands is further proved by novel iridescence tests.

Percolation of sulfide liquid through semi-consolidated silicate cumulates: Textural evidence from breccia ores in the Kalatongke Cu-Ni sulfide deposit, NW China

The Kalatongke Cu-Ni sulfide deposit is an important Ni producer in China and contains abundant breccia ores which are especial in that the silicate fragments enclosed within the sulfide matrix have similar mineral assemblages to the host norite body. Using a combination of microbeam X-ray fluorescence (μ-XRF) and Tescan integrated mineral analyzer (TIMA) mapping, and 3D morphology by high-resolution X-ray computed tomography (HRXCT), we show that the breccia ores are of magmatic origin, as there are no foliation and fabrics of silicate fragments in the sulfide matrix. The 3D morphology of the breccia ores reveal that large silicate fragments are continually connected, whereas small silicate fragments are sub-spheric to spheric with sphericity values close to 1 and commonly rimed by magnetite. All these textures can be explained by that semi-consolidated silicate cumulates were percolated by sulfide liquid from replenished sulfide-bearing magma pulse in the magma conduits. The sulfide liquid from the replenished magma may have accumulated to form a sulfide pool overlying the semi-consolidated cumulates. Due to its high density, the sulfide liquid in the pool could percolate downward and infill the fracture network in the semi-consolidated cumulates, forming sulfide networks in the breccia ores. The sulfide liquid may also trap the interstitial, silicate melts on its way downward throughout the semi-consolidated cumulates, forming small sub-spheric to spheric silicate fragments in the breccia ores. Such a process revealed by the texture of breccia ores indicates that replenished magma pulses and degrees of percolation of sulfide liquid through semi-consolidated cumulates essentially control the distribution of ore bodies in the Kalatongke deposit.

Microbeam X-ray Reanalysis on Periodically Assembled Poly(β-Hydroxybutyric acid-Co-β-hydroxyvaleric acid) Tailored with Diluents.

Self-assembly of 3D interiors and iridescence properties of poly(β-hydroxybutyric acid-co-β-hydroxyvaleric acid) (PHBV) periodic crystals are examined using microcopy techniques and microbeam X-ray diffraction. Morphology of PHBV can be tailored by crystallizing in presence of poly(vinyl acetate) (PVAc) or poly(trimethylene adipate) (PTA) for displaying desired periodicity patterns. The regular alternate-layered lamellae of banded PHBV crystal aggregates, resembling the structures the natural mineral moonstone or nacre, are examined to elaborate the origin of light interference and formation mechanisms of periodic lamellar aggregation of PHBV spherulites. By using PHBV as a convenient model and the crystal diffraction data, this continuing work demonstrates unique methodology for effectively studying the periodic assembly in widely varying polymers with similar aggregates. Grating structures in periodically assembled polymer crystals can be tailored for microstructure with orderly periodicity.

Antigorite Dehydration under Compression and Shear Loadings in a Rotational Diamond Anvil Cell

Mineral dehydration in the subduction zone enormously affects Earth’s geodynamics and the global geochemical cycles of elements. This work uses Raman spectroscopy and X-ray diffraction to investigate the dehydration process of antigorite under compression and shear loading conditions in a rotational diamond anvil cell (RDAC) at room temperature. In order to compare the shear effects, T301 stainless steel and Kapton plastic are applied as the gasket materials. In the experiment using a high-strength T301 stainless steel gasket, two new broad OH-stretching peaks of H2O and H3O2− appear at 3303 and 3558 cm−1, respectively, at 1.7 GPa. The original sharp OH-stretching peaks of antigorite at 3668 and 3699 cm−1 remain, while the central pressure is increased to 8.0 GPa, and the largest pressure gradient is about 2.5 GPa in the sample chamber. In another experiment with a low-strength gasket of Kapton plastic, two new OH-stretching broad peaks of H2O and H3O2− also start to appear at 3303 and 3558 cm−1, respectively, at a lower pressure of 0.3 GPa, but the original sharp OH-stretching peaks of antigorite at 3668 and 3699 cm−1 almost completely vanish as the central pressure reaches 3.0 GPa, with the largest pressure gradient at around 4.8 GPa. The comparison between the two experiments shows that antigorite is easier to dehydrate in the chamber of a Kapton plastic gasket with a larger gradient of shear stress. However, its axial compression stress is lower. The high-pressure Raman spectra of MgO2(OH)4 octahedron and SiO4 tetrahedron in the low wavenumber zones (100–1200 cm−1) combined with the micro-beam X-ray diffraction spectrum of the recovered product strongly support the structural breakdown of antigorite. This investigation reveals that the water-bearing silicate minerals have strong shear dehydration in the cold subduction zone of the plate, which has important applications in predicting the physical and chemical properties of subduction zones and deducing the rate of plate subduction.

X-ray micro-beam characterization of an elastically bent thin diamond plate for x-ray optics applications

Insufficient information on the diffraction and energy-dispersion properties of elastically bent diamond limits its range of application in X-ray optics. Laue micro-beam diffraction has excellent potential for studying these properties. With this method, we explained the origin of the Laue spots asterism, calculated the strain–stress fields generated due to the bending of the diamond plate, and determined the bending radius in situ with high accuracy. The method can be used to control the dispersion characteristics of bent plates by changing the x-ray beam diameter or bending radius. Important conclusions are drawn for practical application of bent diamonds.

Development of High-Energy µ-X-ray Fluorescence and X-ray Absorption Fine Structure for the Distribution and Speciation of Rare Earth Elements in Natural Samples

Micro-X-ray fluorescence and X-ray absorption fine structure (µ-XRF-XAFS) is one of the most powerful tools to identify the distribution and speciation of trace elements in natural samples with µm spatial resolution. However, conventional µ-XRF-XAFS studies applied to rare earth elements (REEs: lanthanide elements + Y in this study) are mainly limited to their L-edges and L lines (except for Y) that are subject to strong interferences from other elements (mainly transition metals). In this study, we extend µ-XRF-XAFS to the higher energy region (HE-µ-XRF-XAFS) by using an incident X-ray microbeam (size: ca. 1 × 1 µm2) between 38 and 54 keV to realize K-edge excitation lanthanide analysis without interferences from other elements at the BL37XU beamline, SPring-8 (Japan). This method enables us to simultaneously analyze (i) REE patterns (from La to Dy), (ii) XAFS spectra, and (iii) µm-scale distribution of each REE in the natural sample. The proposed method also realizes the simultaneous application of µ-XAFS at low (e.g., Fe K-edge) and high (lanthanide K-edges) energy at the same spot without changing the setup of the µ-XRF-XAFS system using the detuning technique.

Effect of a Heterogeneous Network on the Fracture Behavior of Epoxy Resins

Epoxy resins, which possess a three-dimensional network obtained by a curing reaction between epoxy and amine compounds, are in a glassy state at room temperature. They are therefore generally brittle and exhibit rather poor resistance to crack propagation, which is one of the greatest drawbacks for their practical application. To solve this problem, a better understanding of their fracture behavior, which is related to long-term durability, is strongly desired. We herein report on how the extent of network heterogeneity affects the fracture behavior of epoxy resins. Three types of epoxy resins were obtained under different curing conditions, which generated different extents of heterogeneity. The fracture behavior of the three epoxy resins was examined by in situ scanning electron microscopy in conjunction with microbeam X-ray scattering experiments. When the epoxy resin in which a notch was pre-introduced was stretched under a small strain, the internal network structure was deformed, and the extent was more significant with increasing heterogeneity. As further stretching was applied, a crack propagated from the notch. This occurred more easily with increasing heterogeneity. That is, the toughness of the epoxy resins decreased with increasing network heterogeneity. The knowledge obtained here will be useful for understanding and controlling the toughness of epoxy resins.

Scanning Three-Dimensional X-ray Diffraction Microscopy with a Spiral Slit

Recently, nondestructive evaluation of the stresses localized in grains was achieved for plastically deformed low-carbon steel using scanning three-dimensional X-ray diffraction (S3DXRD) microscopy with a conical slit. However, applicable metals and alloys were restricted to a single phase and evaluated stress was underestimated due to the fixed Bragg angles of the conical slit optimized to αFe. We herein propose S3DXRD with a rotating spiral slit adaptable to various metals and alloys and accurate stress evaluation with sweeping Bragg angles. Validation experiments with a 50-keV X-ray microbeam were conducted for low-carbon steel as a body-centered cubic (BCC) phase and pure Cu as a face-centered cubic (FCC) phase. As a result of orientation mapping, polygonal grain shapes and clear grain boundaries were observed for both BCC and FCC metals. Thus, it was demonstrated that S3DXRD with a rotating spiral slit will be applicable to various metals and alloys, multiphase alloys, and accurate stress evaluation using a X-ray microbeam with a higher photon energy within an energy range determined by X-ray focusing optics. In principle, this implies that S3DXRD becomes applicable to larger and thicker metal and alloy samples instead of current miniature test or wire-shaped samples if a higher-energy X-ray microbeam is available.

Observation of Histone H2AX Phosphorylation by Radiation-Induced Bystander Response Using Titanium Characteristic X-ray Microbeam.

Radiation-induced bystander response (RIBR) is a response induced in non-irradiated cells that receive bystander signals from directly irradiated cells. X-ray microbeams are useful tools for elucidating the mechanisms underlying RIBR. However, previous X-ray microbeams used low-energy soft X-rays with higher biological effects, such as aluminum characteristic X-rays, and the difference from conventional X-rays and γ-rays has often been discussed. The microbeam X-ray cell irradiation system at the Central Research Institute of Electric Power Industry has been upgraded to generate higher energy titanium characteristic X-rays (TiK X-rays), which have a longer penetration distance sufficient to irradiate 3D cultured tissues. Using this system, we irradiated the nuclei of HeLa cells with high precision and found that the pan-nuclear induction of phosphorylated histone H2AX on serine 139 (γ-H2AX) in the non-irradiated cells increased 180 and 360 min after irradiation. We established a new method to quantitatively evaluate bystander cells, using the fluorescence intensity of γ-H2AX as an indicator. The percentage of bystander cells increased significantly to 23.2% ± 3.2% and 29.3% ± 3.5% at 180 and 360 min after irradiation, respectively. Our irradiation system and the obtained results may be useful for studies of cell competition as well as non-targeted effects.

Lamellae Grating Assembly in Ring-Banded Spherulites

Despite excruciating attempts by polymer physicists in last several decades, lamellar assembly in ring-banded spherulites (RBSs) is still an unsolved and highly debated puzzle. In an unprecedented manner, the banded rings, based on a model polymer, are mapped with advanced synchrotron microbeam X-ray diffraction. According to the diffraction map and microscopy-dissection morphology, the periodically banded structure is composed of lamellae self-assembled as structural gratings. The comparison of a real-time micrograph with this mapping shows the sequential arrangement and orientation of lamellae in gratings. Lamellar assembly in RBS is fully explained with experimental evidence. This methodology can be applied to a wide variety of polymers to analyze spherulites displaying periodic self-assembled patterns.

Comparison of the dosimetric response of two Sr salts irradiated with 60Co γ-rays and synchrotron X-rays at ultra-high dose rate

As part of the development of innovative radiotherapy techniques using X-ray synchrotron sources, namely FLASH-radiotherapy and microbeam radiation therapy (MRT), two rod dosimeters based on strontium sulfate (SrSO4) and strontium carbonate (SrCO3) were developed and irradiated at the ESRF-ID17 Biomedical beamline to investigate new solid-state dosimeters.The radiation-induced defect in Sr-based dosimeters was detected by means of an electron paramagnetic resonance (EPR) spectrometer. For the study, the EPR response of the dosimeters irradiated with synchrotron X-rays in the 30–600 keV range and dose rate of 11.6 kGy/s was compared with the response after irradiation with a 60Co γ-ray source with a dose rate of 0.288 Gy/s.Both Sr dosimeters show an increased intensity of the EPR signal in the case of irradiation at the synchrotron with respect to the case of 60Co γ-ray irradiation. The measured enhancement of the delivered dose is explained by the fact that Sr shows an increased photoelectric interaction at orthovoltage X-ray energies, producing an increased number of free radicals.The experimental relative response rESRF of the EPR signals between samples irradiated at the ID17 beamline and the 60Co beam quality was found to be 9.66 for SrSO4 and 11.19 for SrCO3. Meanwhile, the theoritical relative responses rμen/ρESRF calculated as the ratio of mass energy absorption coefficients (μen/ρ) of the dosimeters to that for water at the ID17 with respect to the 60Co beam was found to be 11.85 for SrSO4 and 13.31 for SrCO3.The increased EPR response of Sr salt dosimeters irradiated with photons in the keV range proved that these detectors type could be a good candidate for the development of very sensible detectors for radiotherapy applications.

Dislocation density transients and saturation in irradiated zirconium

Zirconium alloys are widely used as the fuel cladding material in pressurized water reactors, accumulating a significant population of defects and dislocations from exposure to neutrons. We present and interpret synchrotron microbeam X-ray diffraction measurements of proton-irradiated Zircaloy-4, where we identify a transient peak and the subsequent saturation of dislocation density as a function of exposure. This is explained by direct atomistic simulations showing that the observed variation of dislocation density as a function of dose is a natural result of the evolution of the dense defect and dislocation microstructure driven by the concurrent generation of defects and their subsequent stress-driven relaxation. In the dynamic equilibrium state of the material developing in the high dose limit, the defect content distribution of the population of dislocation loops, coexisting with the dislocation network, follows a power law with exponent α≈2.2. This corresponds to the power law exponent of β≈3.4 for the distribution of loops as a function of their diameter that compares favourably with the experimentally measured values of β in the range 3≤β≤4.

Multidimensional Profiling of Human Body Hairs Using Qualitative and Semi-Quantitative Approaches with SR-XRF, ATR-FTIR, DSC, and SEM-EDX

This study aimed to assess the potential of a multidimensional approach to differentiate body hairs based on their physico-chemical properties and whether body hairs can replace the use of scalp hair in studies linked to forensic and systemic intoxication. This is the first case report controlling for confounding variables to explore the utility of multidimensional profiling of body hair using synchrotron synchrotron microbeam X-ray fluorescence (SR-XRF) for longitudinal and hair morphological region mapping) and benchtop methods, including attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) (complemented with chemometrics analysis), energy dispersive X-ray analysis (EDX) (complemented with heatmap analysis), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) analysis (complemented by descriptive statistics) to profile different body hairs in terms of their elemental, biochemical, thermal, and cuticle properties. This multidimensional approach provided supportive information to emphasize the intricate and rather complex interplay between the organization and levels of elements and biomolecules within the crystalline and amorphous matrix of different body hairs responsible for the differences in physico-chemical properties between body hairs that are predominantly affected by the growth rate, follicle or apocrine gland activity, and external factors such as cosmetic use and exposure to environmental xenobiotics. The data from this study may have important implications for forensic science, toxicology and systemic intoxication, or other studies involving hair as a research matrix.

A Quantitative Method for the Composition of 7B05 Cast-Rolled Aluminum Alloys Based on Micro-Beam X-ray Fluorescence Spectroscopy and Its Application in Element Segregation of Recrystallization

Microscopic content segregation is among the important reasons for the anisotropy of mechanical properties in the cast-rolled sheets of the 7B05 aluminum alloy. It is of great significance to study the uniformity of aluminum alloys in terms of the microscopic composition and structure. In this study, a precise method for composition quantification based on micro-beam X-ray fluorescence spectroscopy is established by parameter optimization and a calibration coefficient. Furthermore, this method was applied for exploring and quantifying the relationship between recrystallization and deformation microstructures. The results show that the comprehensive measurement effects of all elements are the best when the X-ray tube voltage is 50 kV, the current is 150 μA, and the single-pixel scanning time is 100 ms. After verification, the sum of differences between the measured values and the standard values for all elements using the calibration coefficient is only 0.107%, which confirms the accuracy of the optimized quantitative method. Three types of segregation indexes in national standards were used to capture small differences, and finally ensure that the segregation degrees of elements are Ti > Fe > Cr > Cu > Mn > Zr > Zn > Al. The quantitative segregation results obtained by the spatial-mapping method show that the difference in the content of Al and Zn is approximately 0.2% between the recrystallization region and the deformation region, the difference in the content of Fe and Ti is 0.018% and 0.013%, the difference in the content of Cr, Cu and Zr is approximately 0.01%, and the difference in the content of Mn is not obvious, only 0.004%.

Microscopic and Small-/Wide-Angle Microbeam X-ray Analyses on Dendritic Crystals in Poly(butylene succinate)

A unique composite dendritic spherulite is detected in a specific crystallization temperature range (Tc = 60–78 °C), whose assembly is probed using microscopy techniques and powerful synchrotron X-ray microbeam analyses. Composite dendritic spherulites composed of feather-like and fern-like branches in poly(butylene succinate) (PBSu) crystallized with poly(ethylene oxide) diluent are analyzed on top surface morphologies correlating with interior-dissected assembly, concurrently through polarized-light optical microscopy, scanning electron microscopy, and synchrotron-radiation X-ray microbeam analysis. The feather-like branch is composed of fully edge-on crystal plates, while the fern-like branch is composed of flat-on crystal plates. These branches originate from a common nucleus with different growth rates. For the first time, the dendritic PBSu spherulite serves as a convenient model for understanding the mechanisms how edge-on and flat-on crystal orientations can alternate not only in a serial mode to form ring bands but also in a parallel mode to form straight dendrites. Morphology evidence and detailed microbeam techniques collectively prove that these discontinuous lamellar plates discretely and gradually tilt and bend to transform from a vertical to a horizontal crystal plate with a corresponding alteration in birefringence.

Gas-mediated trace element incorporation into rhyolite-hosted topaz: A synchrotron microbeam XAS study

Abstract Magmatic gas exsolving during late-stage cooling of shallow magmas has been considered an important facilitator of low-pressure alteration and metal transport. However, the chemical properties of such gas, particularly its metal transport mechanisms and capacity, remain elusive. Trace elements in minerals produced by gas-mediated surface reaction or precipitation from gas capture details of gas composition and reaction pathways. However, interpretation of mineral trace element contents is dependent on understanding crystallographic controls on gas/mineral partitioning. This work investigates the structural accommodation of As, Mn, Ga, Ge, Fe, and Ti in vapor-deposited topaz of vesicular topaz rhyolite from the Thomas Range, Utah, through single-crystal synchrotron microbeam X-ray techniques on picogram quantities of those trace elements. X-ray absorption near edge structure (XANES) data indicates that these elements are incorporated into topaz as As5+, Fe3+, Mn3+, Ti4+, Ga3+, and Ge4+. Extended X-ray absorption fine structure (EXAFS) analysis for these trace elements, compared to EXAFS of structural Al and Si, reveals that As5+ and Ge4+ are incorporated directly into the tetrahedral site of the topaz structure, with the octahedral site accommodating Mn3+, Fe3+, Ga3+, and Ti4+. For As5+ and Fe3+, the structural impact of substitution extends to at least second neighbors (other elements were only resolvable to first neighbors). Further interpretation of the EXAFS results suggests that the substitution of Ti4+ results in increased distortion of the octahedral site, while the other trace elements induce more uniform expansion correlating in magnitude to their ionic radius. Comparison of quantified X-ray fluorescence (XRF) data for two topaz crystals from this rhyolite reveals variable trace element concentrations for As5+, Fe3+, Ga3+, and Ti4+, reflective of a source gas undersaturated in these trace elements changing in concentration over the period of topaz deposition. The identical Ge4+ content of the two topaz crystals suggests that Ge4+ in the gas was buffered by the growth of another Ge4+-bearing phase, such as quartz. The very low Mn3+ content in the topaz crystals does not reflect the abundance of Mn3+ in the gas (saturation of Mn is evidenced by coexisting bixbyite). Instead, it suggests a strong Jahn-Teller inhibitory effect to the substitution of Mn3+ for Al3+ in the distorted octahedral site of topaz. It is proposed that exsolution of an HF-enriched gas from cooling rhyolitic magma led to local scouring of Al, Si, and trace metals from the magma. Once topaz crystals nucleated, self-catalyzed reactions that recycle HF led to continued growth of topaz.