Natural Olivine Research Articles

Hydrogen, trace, and ultra-trace element distribution in natural olivines

We investigate the coupling between H, minor, trace, and ultra-trace element incorporations in 17 olivines from ten different locations covering various petrological origins: magmatic, hydrothermal, and mantle-derived context. Concentrations in major element are determined by micro X-ray fluorescence. Minor, trace, and ultra-trace elements are determined by laser ablation inductively coupled plasma mass spectrometry. Hydrogen concentrations are quantified using unpolarized and polarized Fourier transform infrared spectroscopy (FTIR). Forsterite contents (83.2–94.1%) reflect the petrogenetic diversity. Hydrogen concentrations range from 0 to 54 ppm H2O wt. Minor element concentrations (Ni + Mn) range from 3072 to 4333 ppm, and impurities are dominated by Ni, Mn, Ca or B. Total trace element concentrations range from 8.2 to 1473 ppm. Total rare Earth and extended ultra-trace elements concentrations are very low (< 0.5 ppm). Magmatic and hydrothermal olivines show the most and least amount of impurities, respectively, and mantle-derived olivines have concentrations between these two extremes. Combined with minor, trace, and ultra-trace element concentrations, the hydrogen concentrations, and FTIR OH bands reflect the point defect diversity imposed by different geological settings. Hydrogen concentrations are inversely correlated with divalent impurities, indicating their competition for vacancies. However, a broad positive correlation is also found between OH bands at 3575 and 3525 cm−1 and Ti, confirming the existence of Ti-clinohumite-like point defect in mantle olivines. Nonetheless, Ti does not exclusively control hydrogen incorporation in olivine due to the co-existence with other mechanisms, and its effect appears diluted. Our results confirm that hydrogen behaves as a peculiar incompatible element, and furthermore as an opportunistic impurity in olivine.

Are the thermodynamic properties of natural and synthetic Mg2SiO4-Fe2SiO4 olivines the same?

Abstract It is not known if the thermodynamic behavior of some minerals and their synthetic analogues are quantitatively the same. Olivine is an important rock-forming substitutional solid solution consisting of the two end-members forsterite, Mg2SiO4, and fayalite, Fe2SiO4. We undertook the first heat capacity, CP, measurements on two natural olivines between 2 and 300 K; nearly end-member fayalite and a forsterite-rich crystal Fo0.904Fa0.096. Their CP(T) behavior is compared to that of synthetic crystals of similar composition, as found in the literature. The two natural olivines are characterized by X-ray powder diffraction and 57Fe Mössbauer spectroscopy. The X-ray results show that the crystals are well crystalline. The Mössbauer hyperfine parameters, obtained from a fit with two Fe2+ quadrupole split doublets, are similar to published values measured on synthetic olivines. There are slight differences in the absorption line widths (i.e., FWHM) between the natural and synthetic crystals. CP (2 to 300 K) is measured by relaxation calorimetry. The CP results of the natural nearly end-member fayalite and published values for two different synthetic Fa100 samples are in excellent agreement. Even CP resulting from a Schottky anomaly and a paramagnetic-antiferromagnetic phase transition with both arising from Fe2+ are similar. There are slight differences in the Néel temperature between the natural 63 K and synthetic ~65 K fayalites. This is probably related to the presence of certain minor elements (e.g., Mn2+) in the natural crystal. The third-law entropy, S°, value is 151.6 ± 1.1 J/(mol·K). CP behavior of the natural forsterite, Fo0.904Fa0.096, and a synthetic olivine, Fo90Fa10, are in excellent agreement between about 7 and 300 K. The only difference lies at T &amp;lt; 7 K, as the former does not show Debye T3 behavior, but, instead, a plateauing of CP values. The S° value for the natural forsterite is 99.1 ± 0.7 J/(mol·K).

Shear deformation of nano- and micro-crystalline olivine at seismic slip rates

Several thermally activated mechanisms have been proposed to explain the dynamic weakening of faults at fast, seismic slip rates v > 0.1 m s−1. Nevertheless, direct constraints from microstructural observations on the operation of such weakening mechanisms are still lacking for most rock forming minerals. This includes olivine, a very refractory mineral relevant for seismic activity occurring in peridotite massifs. Here, we report mechanical data and microstructures of olivine aggregates deformed in a rotary shear apparatus at slip rates from 10−2 m s−1 to 1 m s−1. A number of 34 shear deformation experiments were performed under axial stresses of 20 MPa and at room temperature. Samples are composed of either synthetic iron-free nanocrystalline forsterite powder (initial grain size = 0.07 μm) or natural iron-bearing olivine powder from San Carlos or San Bernardino (Fo91, Arizona, USA; initial grain size = 70 ± 2 μm). Shear deformation lasts from a few seconds up to 5 min and ends after 0.03 to 3 m of slip. Independently of the initial grain size or composition, friction coefficients decrease from peak values of 0.8 to values below 0.4, after only 0.1 m of slip. The recovered samples were characterized by scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. For all samples, before the onset of dynamic weakening, the deformation localizes in a principal shear zone, well-marked in the natural olivine aggregates by a rapid decrease of grain size down to <1.7 μm. Variations in texture, fractured grains and the formation of a fine-grained matrix support cataclastic flow at an early stage of deformation, responsible for the foremost grain size reduction. The samples display well-defined zones with partially sintered microstructure, and shape preferred orientation. The initial texture of the cold-pressed starting material is rapidly reduced to a near random distribution after only 0.03 m of slip. All crystal preferred orientations (CPO) remain weak, with a J-index ≲2. Based on the microstructures, the dominant deformation mechanism may be enhanced effective diffusion (by surface and grain boundary diffusion) causing mechanical weakening and a viscous behavior, which is then temperature-dependent under sub-solidus conditions. We find no microstructural evidence for frictional melting, flash heating or thermal decomposition. Our results advocate that dynamic weakening of faults is independent of initial grain size, and can be achieved after displacements as low as 0.1 m without production of frictionally induced-melt.

Behavior and origin of hydrogen defects in natural orthopyroxene during high-temperature processes

Abstract Spectral features of hydrogen defects in natural mantle minerals derive from physico-chemical conditions of the lithosphere. Although hydrogen defects in synthetic orthopyroxene have been well investigated, their complex spectral features in natural orthopyroxenes are still difficult to decipher. To clarify this issue, it is indispensable to reveal what happens to hydrogen defects during high-temperature processes, thereby fingerprinting the origins of hydrogen defects observed in natural orthopyroxene. Here, we carry out Fourier transform infrared spectroscopic studies on hydrogen defects of three natural orthopyroxenes at elevated temperatures to 1000 °C. Hydrogen defects display reversible disordering at temperatures above 700 °C, which is different from those at ambient conditions. Moreover, hydrogen diffusivities are significantly different between the orthopyroxene samples from different tectonic settings despite their similar iron contents. Even for the same crystal, different hydrogen defects display different diffusion behaviors. Hydrogen defects corresponding to the 3420 cm−1 band have the fastest diffusivity relative to the other hydrogen defects. Most importantly, hydrogen defects can redistribute in the crystal, with new hydrogen defects produced at the cost of the initial hydrogen defects rather than involving a reaction with an external hydrogen source. Combining these findings with previously reported hydrogen defects in natural olivine and clinopyroxene at high temperatures, we propose that: (1) to correctly relate hydrogen defects features to geological processes, it is imperative to understand their behavior and origin, and (2) hydrogen disordering should be taken into account when predicting and extrapolating data on physical properties of the mantle from room-temperature measurements.

Investigation of the crystal structure of a low water content hydrous olivine to 29.9 GPa: A high-pressure single-crystal X-ray diffraction study

AbstractOlivine is the most abundant mineral in the Earth's upper mantle and subducting slabs. Studying the structural evolution and equation of state of olivine at high-pressure is of fundamental importance in constraining the composition and structure of these regions. Hydrogen can be incorporated into olivine and significantly influence its physical and chemical properties. Previous infrared and Raman spectroscopic studies indicated that local structural changes occur in Mg-rich hydrous olivine (Fo ≥ 95; 4883–9000 ppmw water) at high-pressure. Since water contents of natural olivine are commonly &amp;lt;1000 ppmw, it is inevitable to investigate the effects of such water contents on the equation of state (EoS) and structure of olivine at high-pressure. Here we synthesized a low water content hydrous olivine (Fo95; 1538 ppmw water) at low SiO2 activity and identified that the incorporated hydrogens are predominantly associated with the Si sites. We performed high-pressure single-crystal X-ray diffraction experiments on this olivine to 29.9 GPa. A third-order Birch-Murnaghan equation of state (BM3 EoS) was fit to the pressure-volume data, yielding the following EoS parameters: VT0 = 290.182(1) Å3, KT0 = 130.8(9) GPa, and K′T0 = 4.16(8). The KT0 is consistent with those of anhydrous Mg-rich olivine, which indicates that such low water content has negligible effects on the bulk modulus of olivine. Furthermore, we carried out the structural refinement of this hydrous olivine as a function of pressure to 29.9 GPa. The results indicate that, similar to the anhydrous olivine, the compression of the M1-O and M2-O bonds are comparable, which are larger than that of the Si-O bonds. The compression of M1-O and M2-O bonds of this hydrous olivine are comparable with those of anhydrous olivine, while the Si-O1 and Si-O2 bonds in the hydrous olivine are more compressible than those in the anhydrous olivine. Therefore, this study suggests that low water content has negligible effects on the EoS of olivine, though the incorporation of water softens the Si-O1 and Si-O2 bond.

Rates of Olivine Grain Growth During Dynamic Recrystallization and Postdeformation Annealing

AbstractWe performed deformation and grain growth experiments on natural olivine aggregates with olivine water contents (COH = 600 ± 300 H/106 Si) similar to upper mantle olivine, at 1000–1200°C and 1,400 ± 100 MPa confining pressure. Our experiments differ from published grain growth studies in that most were (1) conducted on natural olivine cores rather than hot‐pressed aggregates and (2) dynamically recrystallized prior to or during grain growth. We combine our results with similar experiments performed at 1200–1300°C and fit the data to a grain growth relationship, yielding a growth exponent (p) of 3.2, activation energy (EG) 620 ± 145 kJ mol−1 (570 ± 145 kJ mol−1 when accounting for the role of temperature on water content), activation volume (VG) ~5 × 10−6 m3 mol−1, and rate constant (k0) 1.8 × 103 mp s−1. Our EG is within uncertainty of that predicted for dislocation creep of wet olivine (E* = 480 ± 40 kJ mol−1). Grain size in strain rate‐stepping samples adjusted to the olivine piezometer within 1.3–7.9% strain. The active grain boundary migration processes during deformation and dynamic recrystallization affect the kinetics of postdeformation grain growth, as grain boundary migration driven by strain energy density (ρGBM) may delay the onset of grain growth driven by interfacial energy (γGBM). We compared our postdeformation grain growth rates with data from previously published hydrostatic annealing experiments on synthetic olivine. At geologic timescales, the growth rates are much slower than predicted by the existing wet olivine grain growth law.

Effect of pressure on the kinetics of peridotite serpentinization

The kinetics of serpentinization were investigated at 400–500 °C and 3.0–20 kbar using natural olivine and peridotite for run durations of 9–38 days. The serpentine varieties were lizardite for all the experiments. The serpentinization kinetics at 400 °C and 3.0 kbar and at 500 °C and 20 kbar displayed a sigmoidal kinetic behavior, with very sluggish reaction rates at the early stage of serpentinization, followed by a sudden increase in the reaction rates. They were 1–2 orders of magnitude faster than serpentinization kinetics commonly used for modeling serpentinization-related processes. Pressure greatly increases the rates of peridotite serpentinization at 500 °C, e.g., 19% of reaction extent was achieved within 20 days for experiments at 500 °C and 3.0 kbar with starting grain sizes of < 30 μm, which increased to 96% for experiments at 500 °C and 20 kbar over the same period. Compared to olivine, peridotite was serpentinized at much faster rates at 400–500 °C and 3.0 kbar, reflecting the influence of pyroxene and spinel. Pyroxene minerals released some of its SiO2 during serpentinization, which was involved in the serpentinization of olivine, supported by larger amounts of SiO2 in olivine-derived serpentine compared to those of primary olivine. Thermodynamic calculations suggest that Gibbs energy of olivine hydrolysis decreases greatly with increasing pressures, and it becomes negative at 400–500 oC and 3.0–20 kbar with the involvement of silica. The experimental results of this study may be applied to natural geological settings where abundant H2O is present.

Multi-Stage Magma Evolution in Intra-Plate Volcanoes: Insights From Combined in situ Li and Mg–Fe Chemical and Isotopic Diffusion Profiles in Olivine

Olivines from two locations in the Massif Central volcanic region (France) have been investigated and lithium chemical and isotopic profiles have been determined. The shape and orientation of both the chemical and isotopic profiles indicate that they were dominantly generated by Li diffusion into and within the olivine grains during magmatic evolution and could be modeled in combination with existing Mg and Fe isotope inter-diffusion profiles. Extremely low δ7Li-values down to -30.7 ‰ (relative to IRMM-16) in the crystal core region and elevated values at the crystal rims (δ7Li ~8 to 10 ‰), along with increasing concentrations from cores (~3 to 1 µg/g) towards the rim (12 to 6 µg/g) have been found. While Mg-Fe isotope and chemical profiles have been modeled by a single diffusive event (Oeser et al., 2015), concentration and isotope profiles of the fast-diffusing Li indicate a second diffusive event, which is not detectable by the slower Mg-Fe exchange diffusion couple. Time scales of the first diffusion event were taken from Oeser et al. (2015) based on Mg-Fe isotopic exchange diffusion modeling with well-determined diffusion coefficients which have been interpreted as the residence time of the olivine crystals in a magma chamber. This first event also generated the low δ7Li observed in olivine cores. Comparison of the length of the Mg-Fe and Li profiles could thus be used to determine the less well-known diffusion coefficients of Li in the studied olivine crystals. This latter event might represent a more short-lived degassing process, related to the ascent of the magma prior to eruption. Such a process would only affect Li, which behaves volatilely during degassing, but not the refractory elements Fe and Mg. The findings of this study show that the combined use of isotopic diffusion systems with different diffusion rates, i.e. of spatially resolved δ7Li and Mg-Fe isotope diffusion profiles, is a powerful tool to model even multi-stage evolution processes in a magmatic system. Potentially, Li diffusion, at typically low Li concentration levels in natural olivine, is coupled to that of other slower-diffusing elements, which is not the case at higher concentration levels in laboratory experiments.

Present-day volcanism on Venus as evidenced from weathering rates of olivine.

At least some of Venus' lava flows are thought to be <2.5 million years old based on visible to near-infrared (VNIR) emissivity measured by the Venus Express spacecraft. However, the exact ages of these flows are poorly constrained because the rate at which olivine alters at Venus surface conditions, and how that alteration affects VNIR spectra, remains unknown. We obtained VNIR reflectance spectra of natural olivine that was altered and oxidized in the laboratory. We show that olivine becomes coated, within days, with alteration products, primarily hematite (Fe2O3). With increasing alteration, the VNIR 1000-nm absorption, characteristic of olivine, also weakens within days. Our results indicate that lava flows lacking VNIR features due to hematite are no more than several years old. Therefore, Venus is volcanically active now.

Forming Olivine Phenocrysts in Basalt: A 3D Characterization of Growth Rates in Laboratory Experiments

Our current knowledge of the genesis, ascent, storage and eruption of mafic magmas is intimately linked with olivine, its primary crystal cargo. Recent claims that phenocryst-size crystals can grow rapidly and non-concentrically are challenging our perception of what olivine zoning represents (e.g. controlled by growth and/or diffusion), and whether accurate magma crystallization and diffusion timescales can be retrieved. A series of cooling experiments was carried out in order to quantify the kinetics of olivine growth as a function of the degree of undercooling, and to characterize morphological changes occurring with time. Growth rates estimated via 3D microtomography renderings of experimental crystals attain 10-7 m/s, and are found to be almost an order of magnitude higher than those calculated using 2D sections of the same experiments. We show that mm-sized crystals similar to those found in natural Kilauea samples can be produced after a few hours under moderate undercooling conditions (25-60°C). Growth rates decrease faintly with time, accompanying transitions between skeletal/hopper and more polyhedral morphologies. Growth rates generally increase up to -ΔT=40°C, and decrease slightly at -ΔT=60°C as rates of nucleation likely increase. The -ΔT=40°C vicinity may therefore represent a thermal ‘sweet spot’ for the formation of phenocrysts. Olivine overgrowths on crystals that survived initial dissolution grow slower than homogeneously-nucleated crystals, illustrating how new and old crystals in natural magmas likely respond differently to a thermal perturbation. We suggest that the main growth direction of natural olivine (a or c) may be a sensitive function of undercooling and the presence of a pre-existing growth substrate. Olivine grows faster along the a-axis under moderate to high undercooling conditions, while preferred development along the c-axis likely occurs under lower undercooling conditions and/or as rims grow around existing crystals. The early history of skeletal olivine crystals is controlled by diffusion in the melt (diffusion-controlled growth regime), while their long-term compositional zoning history is mainly controlled by diffusive reequilibration in the crystal.

Influence of pH on Molecular Hydrogen (H2) Generation and Reaction Rates during Serpentinization of Peridotite and Olivine

Serpentinization produces molecular hydrogen (H2) that is capable of supporting communities of microorganisms in hydrothermal fields, which suggests that serpentinization may be closely related to the origin of life at the early history of the Earth and possibly other planets. In this study, serpentinization experiments were performed at 300 °C and 3.0 kbar with natural olivine and peridotite as starting reactants to quantify the influence of acidic and alkaline solutions on the processes of serpentinization. The results reveal that acidic and alkaline solutions greatly influence molecular hydrogen (H2) generation and the rates of serpentinization. Acidic (pH = 2.50) and alkaline solutions (pH = 13.5) increased H2 production and the rates of peridotite serpentinization. Highly acidic solutions (2 M HCl), however, decreased the production of H2 after peridotite serpentinization by around two orders of magnitude. The decrease in H2 production was associated with a sharp decline in the rates of reaction; e.g., when peridotite was reacted with neutral solutions (0.5 M NaCl), 88% of reaction progress was achieved after an experimental duration of 27 days, and the reaction extent decreased by ~50% for experiments with highly acidic solutions (2 M HCl) over the same period. In contrast, for experiments with solely olivine, highly acidic solutions (2 M HCl) promoted the rates of olivine serpentinization and H2 production. The contrasting effect of highly acidic solutions (2 M HCl) on the processes of olivine and peridotite serpentinization may reflect the influence of pyroxene minerals, which could release SiO2 during peridotite serpentinization and, consequently, hydrogen generation and reaction rates may decrease. The experimental results of this study suggest that H2 production and the rates of serpentinization can be greatly influenced by acidic and alkaline solutions and co-existing minerals (e.g., pyroxene).

Space weathering by simulated micrometeorite bombardment on natural olivine and pyroxene: A coordinated IR and TEM study

We studied space-weathering effects caused by micrometeorite bombardment simulated by pulsed intense infrared laser, generating ∼15 mJ per pulse in high vacuum. For our investigation, we selected a natural olivine (San Carlos olivine (Fo91)) and a natural pyroxene (Bamble orthopyroxene (En87)) as important rock forming minerals of the Earth upper mantle as well as key planetary minerals. Irradiated areas of powdered pressed samples were examined by optical reflection spectroscopy in a broad optical and infrared wavelength range (visible-, near-, and mid-infrared) and transmission electron microscopy to identify changes due to micrometeorite impacts. The present study aims to investigate especially the effects of micrometeorite bombardment on reflectance spectra in the mid-IR in preparation for future space missions, as well as for the MERTIS experiment onboard the BepiColombo mission.For both irradiated samples, we found a reduction in albedo and in the reflectance of characteristic Reststrahlen bands and an increase of the transparency feature. VIS and NIR spectra of both minerals show the typical darkening and reddening as described for other space-weathered samples. TEM studies revealed that space-weathered layers in olivine and pyroxene differ in their respective thickness, ∼450 nm in olivine, 100-250 nm in pyroxene, as well as in developed “nanostratigraphy” of laser-ablated material, like nanophase iron (npFe).In conclusion, our spectral and structural findings were compared to samples in which space weathering was caused by different processes. A comparison with these data demonstrates that there is no difference in optical reflectance spectroscopy, but a significant difference in the microstructure of minerals due to the weathering source in space, as there are solar wind and solar flares cause other structural and chemical changes as the bombardment with micrometeorites.

Phosphorus and aluminum zoning in olivine: contrasting behavior of two nominally incompatible trace elements

Phosphorus zoning in olivine is receiving considerable attention for its capacity to preserve key information about rates and mechanisms of crystal growth. Its concentration can vary significantly over sub-micron spatial scales and form intricate, snowflake-like patterns that are generally attributed to fast crystal growth. Ostensibly similar aluminum enrichment patterns have also been observed, suggesting comparable incorporation and partitioning behavior for both elements. We perform 1-atm crystallization experiments on a primitive Kīlauea basalt to examine the formation of P and Al zoning as a function of undercooling − ΔT (− ΔT = Tliquidus − Tcrystallization) during olivine growth. After 24 h spent at Tinitial = 1290 °C (10 °C above olivine stability), charges are rapidly cooled to final temperatures Tfinal = 1220–1270 °C, corresponding to undercoolings − ΔT = 10–60 °C (with Tliquidus = 1280 °C). Compositional X-ray maps of experimental olivine reveal that only a small undercooling (≤ 25 °C) is required to produce the fine-scale enrichments in P and Al associated with skeletal growth. Concentration profiles indicate that despite qualitatively similar enrichment patterns in olivine, P and Al have contrasting apparent crystal/melt mass distribution coefficients of $$K_{\text{P}}^{{{\text{ol}}/{\text{melt}}}}$$ = 0.01‒1 and $$K_{\text{P}}^{{{\text{ol}}/{\text{melt}}}}$$ = 0.002‒0.006. Phosphorus can be enriched by a factor > 40-fold in the same crystal, whereas Al enrichment never exceed factors of 2. Glass in the vicinity of synthetic and natural olivine is usually enriched in Al, but, within analytical uncertainty, not in P. Thus, we find no direct evidence for a compositional boundary layer enriched in P that would suffice to produce P enrichments in natural and synthetic olivine. Numerical models combining growth and diffusion resolve the conditions at which Al-rich boundary layers produce the observed enrichment patterns in olivine. In contrast, the same models fail to reproduce the observed P enrichments, consistent with our observation that P-rich boundary layers are insignificant. If instead, P olivine/melt partitioning is made to depend on growth rate, models adequately reproduce our observations of 40-fold enrichment without boundary layer formation. We surmise that near-partitionless behavior ( $$K_{\text{P}}^{{{\text{ol}}/{\text{melt}}}}$$ close to 1) of P is related to the olivine lattice being perhaps less stiff in accommodating P during rapid crystallization, and/or to enhanced formation of vacancy defects during fast growth. Our results confirm that P is a robust marker of initial rapid growth, but reveal that the undercooling necessary to induce these enrichments is not particularly large. The near-ubiquitous process of magma mixing under volcanoes, for instance, is likely sufficient to induce low-to-moderate degrees of undercooling required for skeletal growth.

Coupled inter-site reaction and diffusion: Rapid dehydrogenation of silicon vacancies in natural olivine

Abstract Natural olivine from Zermatt (Switzerland) and Almklovdalen (Norway) were dehydrogenated at 1 bar, 517–1009 °C at various oxygen fugacity conditions. Following experiments, H contents (either bulk, or core-rim profiles) were measured using Fourier transform infrared spectroscopy, and spectra were resolved into Gaussian peaks. The starting olivine contained ∼150 and ∼10 wt. ppm H2O for the Zermatt and Almklovdalen samples respectively, but importantly the initial H distribution in both corresponded to defects with 4H+ occupying Si vacancies. Experiments in pure forsterite Padron-Navarta and Hermann, (2017) showed that this defect diffuses very slowly relative to other H diffusion mechanisms in olivine. Conversely, we show that, in the Almklovdalen samples, H loss from the Si-vacancy defect can be extremely rapid, and approaches the fastest known mechanism of H diffusion (proton-polaron diffusion) in olivine. The rate of dehydrogenation from the Zermatt olivine is slightly slower, more consistent with the diffusivity of hydrogenated M-site vacancies. The sum of all defects, along with the integrated area of the main Si vacancy peak (3612 cm−1) generally shows simple diffusive behaviour, whereas profiles (or maps) resolved into individual peaks reveal complex profile shapes not consistent with a simple out-diffusion mechanism. This behaviour can be modeled as a combination of inter-site reaction and diffusion, whereby H leaves the tetrahedral site, moves into a faster diffusion pathway, then rapidly exits the crystal. The rate of H loss from, or gain into, olivine can therefore be either diffusion limited, reaction limited, or a combination of the two. This may explain current discrepancies between experiments conducted under different conditions and between experimental and natural data, including the recent observation that H stored in Si vacancies in metamorphic olivine may be retentive over millions of years, despite the capability to diffuse rapidly via a different mechanism.

Natural forsterite strongly enriched by arsenic and phosphorus: chemistry, crystal structure, crystal morphology and zonation

Unusual variety of forsterite strongly enriched by pentavalent constituents, phosphorus and arsenic (up to 12.9 wt% P2O5 and up to 16.0 wt% As2O5) was found in sublimates of the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia, in association with As- and P-depleted forsterite, anhydrite, diopside, hematite, spinel, hauyne, fluorapatite, svabite, berzeliite, calciojohillerite, and arsenudinaite. This forsterite is the P-richest natural olivine which also demonstrates first case of As incorporation in an olivine-type silicate. P- and As-rich forsterite is orthorhombic, space group Pbnm, unit-cell parameters are: a = 4.7762(2), b =10.2643(4), c = 5.9646(2) A and V = 292.41(2) A3. Its crystal structure was solved on single crystal and refined to R = 2.88%. The crystal chemical formula is M(1)(Mg0.83[vac]0.17)M(2)(Mg0.95[vac]0.05)[Si0.56P0.32As0.12]O4. The substitution scheme for the incorporation of pentavalent constituents in forsterite is: VIMg2+ + 2IVSi4+ ↔ VI[vac]0 + 2IVT5+, in which T5+ = P, As and [vac] = vacancy. No sign of vacancies in the tetrahedrally coordinated T site is found.

Trace element analysis of high-Mg olivine by LA-ICP-MS – Characterization of natural olivine standards for matrix-matched calibration and application to mantle peridotites

The trace element composition of olivine is becoming increasingly important in petrological studies due to the ubiquity of olivine in the Earth's upper mantle and in primitive magmatic rocks. The LA-ICP-MS method allows for the routine analysis of trace elements in olivine to sub-ppm levels, but a major drawback of this method is the lack of knowledge about possible downhole fractionation effects when non matrix-matched calibration is used. In this contribution, we show that matrix-matched (i.e., olivine-based) calibration is preferable for small laser spot sizes (<100 μm) due to significant laser-induced inter-element fractionation between olivine and commonly used silicate glass calibration materials, e.g., NIST SRM 612, GSD-1G and BHVO-2G. As a result, we present two Mg-rich natural olivine standards (355OL and SC-GB) that have been characterized by independent methods (EPMA, solution ICP-MS), and by LA-ICP-MS in four different laboratories. These natural olivines have been used 1) as primary standards for the matrix-matched calibration of olivine samples for most elements of interest (e.g., Li, Na, Al, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn), and 2) as secondary standards to assess the accuracy of results. Comparison of olivine- and silicate glass-calibrated results for natural peridotitic olivine reveals that matrix-matched calibration is essential when using small laser spot sizes (<100 μm) in order to mitigate downhole fractionation effects for certain elements, especially Na, P, Mn, Co, Ni and Zn. If matrix-matched calibration is not feasible, we recommend that spot sizes of ≥100 μm, laser fluence of ≤4.0 J/cm2, and total laser shot counts of ≤250 (e.g., 5 Hz repetition rate for 50 s) are used in order to minimize fractionation effects between olivine and silicate glass calibration materials. We demonstrate the applicability of matrix-matched calibration on olivine from a suite of different mantle peridotite xenoliths sampled by kimberlites and alkali basalts from on-craton and off-craton localities.

Rare earth element uptake during olivine/water hydrothermal interaction

Ultramafic-hosted hydrothermal vent systems link the hydrosphere with the peridotitic mantle via serpentinization. Here, the fractionation and mobility of selected trace (Nd, Sm, Gd, Dy, Yb, Sr and Ba) and major cations (Si, Ca, Mg, Fe, Ni) during seawater-peridotite interaction was investigated through a series of experiments where natural olivine grains were reacted with an artificial seawater solution at a range of temperatures (15–90 °C) and grain size distributions. No evidence for any significant olivine dissolution or precipitation of carbonate and, Fe-oxy-hydroxide phases was observed in these experiments. Experimental data show a strong decoupling of REE (Nd, Sm, Gd, Dy, and Yb) from Sr and Ba under all experimental conditions, with Sr and Ba remaining quantitatively in solution. The REE were removed from the solution and were adsorbed onto olivine surface with kinetic rate constants (i.e. uptake over time) that increase with increasing temperature and increasing surface area (i.e. decreasing particle size). Dysprosium and Yb (heavy REE; HREE) were removed from solution with a faster rate than Nd and Sm (light REE; LREE). Gadolinium is decoupled from this trend, with a slower kinetic rate constant than Sm. The activation energies (Ea) of REE adsorption on olivine were higher for Nd and Sm than Dy and Yb. This suggests that the adsorbance of LREE is generally more dependent on temperature than the HREE. The Ea correlates well with the summed 1st, 2nd and 3rd ionization energies of REE suggesting a link between kinetic rates of element adsorption and electron configuration of the 4f-orbitals. Gadolinium has higher Ea than the other analyzed REE, consistent with the electron configuration of Gd3+ where all 4f-orbitals are filled with one electron each. These experimental data suggest that REE are adsorbed on the surface of olivine via inner sphere complexes under low-temperature hydrothermal conditions, when alteration processes are limited or extremely slow. Scavenging and fractionation of REE may occur within the recharge zone of peridotite-hosted hydrothermal systems at relatively low temperatures (<100 °C), leading to fluids with progressively higher LREE/HREE which could impose seawater-derived LREE enrichments in serpentinized peridotites during high temperature, high pressure water/rock interaction deeper in the oceanic lithosphere.

MÖssbauer Study of Changes in Olivine After Heating in Air

Research Article| January 01, 2019 MÖssbauer Study of Changes in Olivine After Heating in Air Mariola Kądziołka-Gaweł; Mariola Kądziołka-Gaweł § Institute of Physics, University of Silesia, 75 Pułku Piechoty 1a, 41-500 Chorzow, Poland § Corresponding author e-mail address: mariola.kadziolka-gawel@us.edu.pl Search for other works by this author on: GSW Google Scholar Zdzisław Adamczyk; Zdzisław Adamczyk Institute of Applied Geology, Silesian University of Technology, Akademicka 2, 44-100 Gliwice, Poland Search for other works by this author on: GSW Google Scholar Lech Kalinowski Lech Kalinowski Institute of Physics, University of Silesia, 75 Pułku Piechoty 1a, 41-500 Chorzow, Poland Search for other works by this author on: GSW Google Scholar Author and Article Information Mariola Kądziołka-Gaweł § Institute of Physics, University of Silesia, 75 Pułku Piechoty 1a, 41-500 Chorzow, Poland Zdzisław Adamczyk Institute of Applied Geology, Silesian University of Technology, Akademicka 2, 44-100 Gliwice, Poland Lech Kalinowski Institute of Physics, University of Silesia, 75 Pułku Piechoty 1a, 41-500 Chorzow, Poland § Corresponding author e-mail address: mariola.kadziolka-gawel@us.edu.pl Publisher: Mineralogical Association of Canada First Online: 17 Jan 2019 Online Issn: 1499-1276 Print Issn: 0008-4476 © 2019 Mineralogical Association of Canada The Canadian Mineralogist (2019) 57 (1): 105–115. https://doi.org/10.3749/canmin.1700074 Article history First Online: 17 Jan 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Mariola Kądziołka-Gaweł, Zdzisław Adamczyk, Lech Kalinowski; MÖssbauer Study of Changes in Olivine After Heating in Air. The Canadian Mineralogist 2019;; 57 (1): 105–115. doi: https://doi.org/10.3749/canmin.1700074 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyThe Canadian Mineralogist Search Advanced Search Abstract The transformation mechanism of Fe2+ cations in two samples of natural olivine (Fe,Mg)2SiO4 after heat treatment in air in the temperature range 400–1180 °C has been studied using 57Fe Mössbauer spectroscopy and XRD measurements. The influence of heating duration (from one to 96 hr) on the behavior of Fe2+ ions in the olivine structure was investigated. Fe3+ ions dominate as a primary product of the thermal treatment in air above 1000 °C. Heating at 1180 °C led to decomposition of the olivine structure. The formation of ferriolivine as a result of low-temperature oxidation was also observed. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Syngas production from biomass gasification in China: A clean strategy for sustainable development

ABSTRACTBiomass gasification, which can be categorized as a set of relatively clean processes, is a good option for hydrogen production. The main purpose of the present work was to focus on the use of natural olivine as a bed material to minimize the tar content and enhance the hydrogen yield. The catalytic gasification tests were carried out in a fluidized bed gasifier using steam as the fluidizing medium. Hydrogen yield slightly increased from 51.9 to 53.1 g/kg biomass, as biomass particle size (BP) decreased from 5.0 to 2.0 mm. The yield of tar also decreased from 0.15 to 0.07 g/Nm3 with BP decreasing from 5.0 to 2.0 mm. With an increase in the catalyst-to-biomass ratio (C/B) from 0.2 to 0.8, HY increased from 47.8 to 51.9 g/kg biomass and tar content (TC) decreased from 0.8 to 0.15 g/Nm3. Temperature and steam/biomass ratio (S/B) were also affected the syngas composition and HY, significantly.

The role of trace elements in controlling H incorporation in San Carlos olivine

We conducted a series of hydroxylation experiments using mm-sized cuboids cut from six different crystals of San Carlos olivine with a range of trace-element concentrations. The cuboids were pre-annealed and then hydroxylated under identical conditions, ensuring that variation in the amounts of H incorporated depended only on the compositional variables. The pre-anneal was at 1400 °C, atmospheric pressure and an oxygen fugacity equivalent to Δlog FMQ + 1, with the subsequent hydroxylation at 800 °C and 1.5 GPa, for 3 days. Hydrogen was incorporated into all six crystals by the four main substitution mechanisms [Si], [Mg], [Ti] and [triv], with homogeneous H contents in the cores of the crystals, indicating H diffusion rates faster than 10− 11 m2/s. Total H as H2O in the homogeneous cores calculated by summing all the infrared absorbance bands ranges from 13 to 27 wt. ppm. The total H2O in the six pre-annealed crystals is poorly correlated with any measured compositional variable. However, when the H2O associated with individual infrared bands is compared, clear trends emerge. The intensity of absorption bands at 3572 and 3525 cm− 1 are strongly correlated with Ti concentrations, whose range in the six crystals exceeds an order of magnitude. Bands between 3400 and 3300 cm− 1, correlate negatively with Na+, but are positively correlated with the difference between molar Cr3+ and Na+. This highlights a previously unrecognised role for Na in suppressing H incorporation in natural olivines. The results confirm the important role that the trace constituents of olivine play in H incorporation. Two of these trace elements, Na and Ti, tend to be similarly enriched or depleted by partial melting or metasomatism of the mantle, but have opposite effects on H incorporation, with Ti enhancing it but Na suppressing it. Models estimating the effect of H in olivine on mantle rheology must, therefore, consider carefully the availability of these trace elements.