Band 96, Heft 11-12

We report on technical improvements in experiments with a deformation-DIA (D-DIA) apparatus, which enable the study of the rheology of solid materials at P-T conditions of the Earth’s mantle transition zone. Dimensions of the anvil truncation, pressure medium, and gasket were optimized to achieve deformation experiments above 13 GPa with a relatively low press load (<0.7 MN) to minimize the damage of the X‑ray transparent second-stage anvils. The adoption of low X‑ray absorbing material (e.g., cubic BN anvils, graphite window in a LaCrO 3 heater) along the X‑ray path enabled quantitative determination of stress and strain of a sample by means of simultaneous in situ X‑ray radial diffraction and radiography using synchrotron radiation at SPring-8. Based on the new technique, a uniaxial deformation experiment with a strain rate of 3.88 × 10 −5 s −1 and strains up to 25.5% was carried out on wadsleyite at a pressure of 14.5 GPa and a temperature of 1700 K.

Lunar granulitic breccias are a group of clast-bearing impact-melt lithologies that have been brecciated, and then metamorphosed at high temperature (-1000 °C) to generate annealed (granoblastic to poikiloblastic) textures. They are ubiquitous among lunar samples, but occur in small volumes, typically as clasts in other lunar rocks. We have determined major, minor, and trace element diffusion profiles in olivines, orthopyroxenes, and clinopyroxenes from one Apollo 16 (60035), three Apollo 17 (77017, 78155, 79215), and two paired lunar meteorites (NWA 3163 and NWA 4881) by means of electron microscopy and electron probe microanalysis. The results show that relic igneous clasts exhibit an absence of, or limited, major element zoning, yet retain minor and trace element profiles. We exploit this characteristic to estimate the duration of high-temperature metamorphism responsible for their recrystallization. To achieve this we have completed pyroxene thermometry, element linescans, X‑ray mapping, and modeling of heating and cooling of hanging wall and footwall lithologies juxtaposed with a hot body. The high equilibration temperatures, moderately high siderophile contents, and time scales of metamorphism of the lunar granulites indicate that they were metamorphosed in relatively near-surface settings. Diffusion calculations indicate that most granulitic breccias were heated for 13 000-300 000 yr. We conclude that they formed above or beneath superheated impact-melt sheets associated with medium-size (100-200 km) craters.

The layer-like crystal structure of franckeite from the mine of San José, Bolivia, exhibits a pronounced one-dimensional transversal wave-like modulation and a non-commensurate layer match in two dimensions. It consists of alternating pseudohexagonal (H) layers and pseudotetragonal (Q) slabs and forms a homologous pair with cylindrite, which has thinner Q slabs. The Q slabs in franckeite are four atomic layers thick. The two components have their own lattices and a common modulation. The Q slab of the refined franckeite structure, Pb 21.74 Sn 9.34 Fe 3.95 Sb 8.08 S 56.87 , is an MS layer (M = Pb 2+ , Sn 2+ , Sb 3+ ) four atomic planes thick, with a = 5.805(8), b = 5.856(16) Å, and the layer-stacking vector c = 17.338(5) Å. The lattice angles are α = 94.97(2)°, β = 88.45(2)°, γ = 89.94(2)°; the modulation vector q = -0.00129(8) a* + 0.128436(10) b* - 0.0299(3) c*. The H layer is a single-octahedron MS 2 layer (M = Sn 4+ , Fe 2+ ) with a = 3.665(8), b = 6.2575(16), c = 17.419(5) Å, α = 95.25(2)°, β = 95.45(2)°, γ = 89.97(2)°; the modulation vector is q = -0.00087(8) a* + 0.13725(16) b* - 0.0314(4) c*. The a and b vectors of both subsystems are parallel; the c vectors diverge. (3+2)D superspace refinement was performed in the superspace group C1, using 7397 observed reflections. It resulted in the overall R(obs) value equal to 0.094. The Q slabs are composed of two tightly bonded double-layers, separated by an interspace hosting non-bonding electron pairs. Average composition of cations on the outer surface was refined as Pb 0.74 (Sn,Sb) 0.26 , whereas that of cations, which are adjacent to the interspace with lone electron pairs, with a configuration analogous to that observed in orthorhombic SnS, corresponds to (Sn,Sb) 0.73 Pb 0.27 . Iron is dispersed over the octahedral Sn 4+ sites in the H layer. Transversal modulation of the Q slab is achieved by local variations in the Pb:(Sn,Sb) ratios at its surface and interior. Its purpose is to re-establish a one-dimensional commensurate contact along [010] between the curved Q and H surfaces to the greatest extent possible. Layer-stacking disorder and divergence of the Q and H stacking directions, and the divergence between modulation wave-front and these stacking directions are typical for the composite structures of franckeite and cylindrite. Because of the increased rigidity of the Q component, franckeite usually forms masses of curved crystals rather than cylindrical aggregates. The existence of this family depends critically on the radius ratios of the cations involved, especially those involving (Pb 2+ , Sn 2+ ) and Sn 4+ . Their replacement by a Pb 2+ :Bi 3+ combination leads to misfit layer structures of a very different type, typified by cannizzarite.

NH4-bearing phases from pre-Permian schists of the Internal Zones of the Betic Cordillera (Spain) have been characterized by X‑ray diffraction, differential thermal analysis and thermogravimetry, infrared spectroscopy, and transmission-analytical electron microscopy. The content and distribution of NH4 in these phases have been estimated by combining elemental analysis of N with mineral quantification based on X‑ray diffraction, whole-rock composition, and electron microprobe data. The obtained results indicate that the NH 4 content in vermiculite ranges between ~0.5 and ~1.0 (wt%), leading to terms with NH 4 > K in the interlayer. The NH 4 content is <0.30 (wt%) in biotite from underlying schists. Muscovite shows very low NH 4 contents (0.04 wt%) through the complete sequence. We interpret that, initially contained in low-grade dioctahedral mica, NH 4 was incorporated in the structure of the trioctahedral phases formed at increasing metamorphic conditions. The entry of NH 4 in the interlayer was favored in chlorite:vermiculite mixed-layered structures and transitional phases with vacancies in the A site (vermiculite) and weak cohesion between layers. NH 4 appears to favor the formation of intermediate phases instead the direct transformation of chlorite to biotite.

We report here the preparation and structural models of alkaline-earth (Ca 2+ , Sr 2+ , Ba 2+ ) and heavy metal (Cd 2+ , Pb 2+ , Ag + ) cation-exchanged natrolites at ambient conditions and compare them to the alkali (Li + , Na + , K + , Rb + , Cs + ) cation forms. The latter two groups all crystallize in the orthorhombic Fdd2 symmetry as the natural sodium natrolite, whereas the alkaline earth analogues are all found in the monoclinic Cc symmetry as scolecite, the natural calcium counterpart. We find the existence of a universal linear relationship between the unit-cell volume and the non-framework cation radius in natrolite. The rotation angles of the fibrous chain units are distributed between 25.5° (Li-form) and 2.9° (Cs-form) to show its inverse proportionality to the non-framework cation radius and the channel opening area. We also propose a possible threshold in the cation radius that dictates the distribution pattern of the non-framework cations and water molecules in the ordered and disordered fashions in natrolite.

We measured hydrogen concentrations in 12 olivines using secondary ion mass spectrometry (SIMS and NanoSIMS), cross-calibrated against Fourier transform infrared (FTIR) spectroscopy and nuclear reaction analysis (NRA). Five of these samples are routinely used for calibration in other laboratories. We assess the suitability of these olivines as standards based on over 300 SIMS analyses, comprising 22 separate calibrations. Seven olivines with 0-125 ppm H 2 O give highly reproducible results; in contrast to previous studies, the data are fit to well-constrained calibration lines with high correlation coefficients (r 2 = 0.98-1). However, four kimberlitic megacrysts with 140-245 ppm H 2 O sometimes yield 16 O 1 H/ 30 Si ratios that have low internal precision and can vary by up to a factor of two even in sequential analyses. A possible cause of this behavior is the presence of sub-microscopic inclusions of hydrous minerals, such as serpentine. In most cases, however, we link the anomalous results to the presence of sub-micrometer to micrometer-scale pores (as small as 100 nm), which we imaged using SEM and NanoSIMS. These pores are interpreted to be fluid inclusions containing liquid H 2 O, other volatiles (including fluorine), and/or hydrous phase precipitates. Ionization of the contents of the pores contributes variably to the measured 16 O 1 H, resulting in analyses with erratic depth profiles and corresponding high uncertainties (up to 16%, 2σ mean ). After filtering of these analyses using a simple criterion based on the error predicted by Poisson counting statistics, all the data fit well together. Our results imply that the Bell et al. (2003) calibration can be applied accurately to all olivines with IR bands from -3400-3700 cm -1 , without the need for band-specific IR absorption coefficients.

Three natural olivines with Fo 80 Fa 20 , Fo 71 Fa 29 , and Fo 62 Fa 38 compositions were investigated in situ at high pressure by single-crystal X‑ray diffraction using a diamond-anvil cell up to -8 GPa at room temperature. The bulk modulus, K T0 , and its first pressure derivative, K′, do not show any significant variation among the compositions investigated and, using the data on a further sample with Fo 92 Fa 8 composition recently investigated in the same laboratory and using the same experimental technique, we obtain, for the first time, a single equation of state for the entire Fo 92 Fa 8 -Fo 62 Fa 38 compositional range. The equation has the following coefficients: K T0 = 124.7(9) GPa and K′ = 5.3(3) and can be used for thermodynamic calculations involving the most common mantle olivine compositions.

As representatives of nominally anhydrous minerals (NAMs) in the crust and mantle the pressuredependent behavior of strontium feldspar and wadsleyite, containing different amounts of water, was studied in a diamond-anvil cell via mid and far IR spectroscopy up to 24 GPa. The samples were synthesized in a piston-cylinder press at 2 GPa/700 °C (strontium feldspar) and in a multi-anvil apparatus at 13.8 GPa/1000 °C (dry wadsleyite) and 13.2 GPa/1150 °C (hydrous wadsleyite). The water content of the samples was determined by polarized FTIR and Raman spectroscopy. The strontium feldspar crystals (up to 300 μm) contained about 1100(100) wt ppm water. The hydrous wadsleyite crystals (up to 240 μm) contained 12 500(900) wt ppm water. The synthesis of dry wadsleyite yielded a fine-grained powder. A new THz/FIR-microscope for the synchrotron source BESSY was developed to conduct the diamond-anvil cell measurements in the far IR region. Conventional in-situ mid IR spectroscopy was also performed on all samples. The measurements on strontium feldspar showed a phase transformation at 6.5(5) GPa (space group I2/c to P21/c). The wadsleyite analyses revealed a phase transition at approximately 8.4(7) GPa in the hydrous and approximately 10.0(7) GPa in the dry sample. It probably represents a transition from an orthorhombic to a monoclinic structure. The high amount of water incorporated in the hydrous wadsleyite shifts the transformation toward lower pressures compared to the dry one. By comparison, the relatively low amount of water in strontium feldspar does not change the stability relations compared to the dry one. Therefore, water incorporation in nominally anhydrous minerals may have an effect on the pressure of phase transitions, whereas the extent of that influence strongly depends on the structure of the phase and the amount of water carried within the mineral.

The coherent dehydration of pure-Mg wadsleyite has been investigated by single-crystal X‑ray diffraction at high temperature and room pressure. Hydrous wadsleyite with 2.8 wt% H 2 O has monoclinic unit-cell parameters of a = 5.6693(4), b = 11.571(1), c = 8.2407(5) Å, b = 90.209(3)°, and V = 540.59(7) Å 3 . Dehydration begins at 635 K with an abrupt increase in the a-axis and decrease in b. After dehydration is complete, the dehydrated sample is orthorhombic with a = 5.6995(3), b = 11.4589(8), c = 8.2556(5) Å, and V = 539.17(6) Å 3 at ambient conditions. Atom position and displacement parameters have been refined for both hydrous and dehydrated wadsleyite samples from intensity measurements conducted at high temperatures. The most significant changes during dehydration are systematic decreases in M2-O1 and M3-O1 bond lengths. After dehydration, M2-O1 and M3-O1 bonds decrease by 3% and 2.5%, respectively. While the length changes of the other M-O bonds are no more than 1%, consistent with the hydration mechanism being protonation of O1. For the monoclinic structure, the average thermal expansion coefficient is 38.4(3) × 10-6 K-1 before dehydration and 28.1(8) × 10 -6 K -1 for the dehydrated sample. The volumetric thermal expansion coefficients for MgO 6 octahedra in the hydrous sample, a0(V), are 36(4), 41(4), 49(5), and 35(4) (10 -6 K -1 ) for M1, M2, M3A, and M3B, respectively. In the dehydrated sample, they are 35(5), 34(4), and 36(2) (10 -6 K -1 ) for M1, M2, and M3, respectively. No significant thermal expansion is observed for SiO 4 tetrahedra of either the hydrous or dehydrated sample.

Experimental data demonstrates that the resorption morphology of diamond greatly depends on the composition of the reacting fluid and can be used to constrain the composition of mantle fluids in diamond source areas and magmatic fluid in kimberlite magma. This requires a model that describes how different fluids interact with the diamond surface. This study uses atomic force microscopy (AFM) to quantitatively characterize the crystallographic orientation of micro-faces that form individual etch pits on diamond surfaces produced naturally in a kimberlite magma and experimentally in H 2 O-rich and CO 2 -rich fluids at 1150, 1250, and 1350 °C and 1 GPa. Dissolution features were examined on {111} diamond faces with the AFM scan areas ranging from 30 × 30 to 1 × 1 μm. The study shows that the extremely different resorption features developed on diamond surface during dissolution in H 2 O- and CO 2 -rich fluids, are formed by the same set of micro-faces with angles ~7, 11, 16, and 22°, corresponding to the {433}, {322}, {221}, and {321} faces, respectively. This suggests that diamond has similar dissolution rates in the same directions of the diamond lattice in both H 2 O- and CO 2 -rich fluid but that the mechanism of material removal is different. Reaction with H 2 O-rich fluid develops regular features due to layer-by-layer carbon removal. In CO 2 -rich fluid, deep etch pits with irregular walls form when dissolution is focused around the outcropping dislocations. The size and shape of the etch pits and their association with the outcropping dislocations depend on temperature and could be used to constrain the crystallization conditions of kimberlite magma. Natural kimberlite-induced resorption features indicate high H 2 O:CO 2 ratios in kimberlitic fluid.

The stacking structure of tubular halloysite, which is easily damaged by electron-beam radiation, has been investigated by high-resolution transmission electron microscopy (HRTEM) using a new TEM with a computer-assisted minimal-dose system. The new TEM is equipped with a high-speed beam blanker by which the specimen is beam-irradiated only during image acquisition by the recording media. Using a few images taken by a CCD camera with a short exposure time (0.04 s), TEM operations such as area search and brightness adjustment are completed by the computer-assisted system, which can decrease the electron dose delivered before recording final HRTEM images by a factor of 100. The specimen used was halloysite (7 Å) with a tubular morphology from Eureka, Nevada, U.S.A. HRTEM images were taken with the incident electron beam perpendicular to the tube axis, which is parallel to the Yi-axes of the dioctahedral 1:1 layer of halloysite. Lattice fringes in halloysite were almost extinguished with an electron dose of -2000 electrons (e)/Å 2 , and it was almost impossible to record crossed lattice fringes without radiation damage using conventional TEMs. By contrast, HRTEM images of high quality and without damage could be recorded with -400 e/Å 2 in the new TEM system. The stacking structures recorded in such images were generally disordered, but ordered packets with one-layer periodicity were often observed. Among them, a stacking sequence that has never previously been observed in kaolinite was identified

In situ X‑ray diffraction experiments were carried out at pressures up to 25 GPa on a synthetic hematite (α-Fe 2 O 3 ) crystal using synchrotron radiation in an angle-dispersive setup. Experiments were performed in diamond-anvil cells using neon as a pressure-transmitting medium. Single-crystal diffraction data were collected from omega scans and structural refinements were carried out for 10 pressure points. Bulk and linear incompressibilities were obtained from least-squares fits of refined data to the Eulerian strain based Birch-Murnaghan equation of state. Finite strain analysis suggests a truncation at second order, yielding results of K 0 = 207(3), Ka 0 = 751(17), and K c0 = 492(8) for bulk and axial moduli, respectively. The a-axis is about 1.5 times stiffer than the c-axis. Compression of the main structural feature, the FeO 6 octahedra, is quite uniform, with just slight changes of distortion parameters at higher pressures.

The IR vibrational properties and the corresponding reflectance spectra of the six most common members of the garnet family (pyrope Mg 3 Al 2 Si 3 O 12 , almandine Fe 3 Al 2 Si 3 O 12 , spessartine Mn 3 Al 2 Si 3 O 12 , grossular Ca 3 Al 2 Si 3 O 12 , uvarovite Ca 3 Cr 2 Si 3 O 12 , and andradite Ca 3 Fe 2 Si 3 O 12 ) were simulated at the ab initio level with the CRYSTAL09 code by using a large all-electron Gaussian-type basis set and the B3LYP hybrid functional. The 17 IR active F1u transverse optical (TO) and longitudinal optical (LO) frequencies, the oscillator strengths, the high frequency and static dielectric constants, and the reflectance spectrum were computed. The agreement with experiments for the TO and LO peaks is always excellent, the mean absolute difference for the whole set of data (overall 178 peaks) being 5 cm -1 . Oscillator strengths, calculated from the mass-weighted effective Born charges, are found in semi-quantitative agreement with the experimental data. The reflectance spectra, simulated through the classical dispersion relation, reproduce the experimental curves extremely well. The availability of the full set of simulated frequencies and intensities, obtained by using uniform computational tools (computer code, variational basis sets, density functional), permits the establishment of correlations between IR wavenumbers and structural features suggested, but only partially documented, in the past

The infrared (IR) spectra of gem-quality xenotime crystals containing considerable amounts of rare earth elements (REEs), are characterized by sharp and strongly pleochroic absorption bands in the 3650-3350 cm -1 region. In contrast, the spectra of partially metamict samples are dominated by a broad band centered at around 3450 cm -1 . Xenotime presents the interesting case of a nominally anhydrous mineral, where the OH stretching frequency region of weakly hydrogen-bonded OH groups is overlapped by absorption bands due to low-energetic f-f electron transitions of REEs, especially of dysprosium. In polarized spectra measured parallel to the c-axis, Dy shows a prominent sharp band at 3519 cm -1 . The assignment of the REE bands is based on the polarized IR spectra of REE doped xenotime single crystals, which have been synthesized by the flux method. A single band at 3480 cm -1 , strongly polarized perpendicular to the c-axis, is assigned to the stretching vibration of an OH group. Deuteration experiments performed at 950 °C prove the assignment of this band and the presence of additional structural OH groups, appearing at annealing temperatures above 500 °C. Models of the OH point defect incorporation into the crystal structure of xenotime can be derived on the basis of fully occupied cation sites and under the assumption of Y- and P-site vacancies. The water content of the gem-quality samples ranges from 5 to 10 wt ppm and for the partially metamict samples from 370 wt ppm to 1.7 wt% H 2 O.

Formation of faujasite- and sodalite/cancrinite-type phases associated with caustic waste reactions in the environment may structurally incorporate contaminant species such as radioactive Sr 2+ and Cs + , and thus provide a mechanism of attenuation. To investigate mineral evolution and structural incorporation of cations in simplified experiments, aluminosilicate solids were precipitated homogeneously at room temperature from batch solutions containing a 1:1 molal ratio of Si to Al and 10 -3 molal Sr and/or Cs, and aged for 30 or 548 days. Syntheses were done with solutions in equilibrium with atmospheric CO 2 and with gas-purged solutions. Experimental products were characterized by bulk chemical analyses, chemical extractions, XRD, SEM/TEM, TGA, solid-state 27 Al NMR, and Sr EXAFS. Chemical analysis showed that solids had a 1:1 Al:Si molar ratio, and that Sr was sequestered at higher amounts than Cs. After 30 days of aging in purged solutions, XRD showed that zeolite X (faujasite-type) was the only crystalline product. After aging 30 and 548 days in solutions equilibrated with atmospheric CO 2 , a mixture of sodalite, cancrinite, and minor zeolite X were produced. Surface areas of solids at 30 days were much lower than published values for zeolite phases synthesized at high temperature, although particle aging produced more crystalline and less aggregated phases with higher bulk surface areas. Characterization of products by 27 Al NMR indicated only tetrahedrally coordinated Al. Measured isotropic shifts of primary resonances did not change substantially with precipitate aging although the primary mineral phase changed from zeolite X to sodalite/cancrinite, indicating local ordering of Al-Si tetrahedra. Analysis of reaction products by Sr EXAFS suggested Sr bonding in hexagonal prisms and six-membered rings of the supercages of zeolite X that may be more site specific than those of monovalent cations. For samples aged for 548 days, interatomic distances from Sr-EXAFS are consistent with partial Sr dehydration and bonding to framework oxygen atoms in sodalite cages or in large channels in cancrinite. Incorporation of Sr into both faujasite and sodalite/cancrinite phases is favored over Cs during room-temperature synthesis, possibly because of increased cation site competition between Cs + and Na + . Results of this study help to constrain cation incorporation into sodalite/cancrinite mineral assemblages that form at caustic waste-impacted field sites and may aid in the predictive modeling of contaminant release.

The electrical conductivity of low albite has been measured using a complex impedance spectroscopic technique at 1.0-3.0 GPa and 773-1073 K in the frequency range of 10 −1 to 10 6 Hz in a YJ-3000t multi-anvil press. Within this frequency range, the complex impedance plane displays a semi-circular arc that represents a grain interior conduction mechanism. The electrical conductivity of albite increases with increasing temperature, and the relationship between electrical conductivity and temperature fits the Arrhenius formula. Pressure has a weak effect on the electrical conductivity of albite in the experimental pressure-temperature (P-T) range in the present work. The pre-exponential factors decrease, and the activation enthalpy increases slightly with increasing pressure. The activation energy and activation volume of albite are 0.82 ± 0.04 eV and 1.45 ± 0.28 cm 3 /mol, respectively. Comparison with previous results with respect to albite indicates that our data are similar to previous data within the same temperature range. The dominant conduction mechanism in albite is suggested to be ionic conduction, where loosely bonded sodium cations, the dominant charge carriers, migrate into interstitial sites within the feldspar aluminosilicate framework. The Na diffusivity inferred from electrical conductivity of albite in this study using the Nernst-Einstein relation is consistent with that of previous studies on natural albite.

The mineralogy and crystal chemistry of apatites occurring in 14 ejecta of historical eruptions (1631 and 1872 A.D.) of the Somma-Vesuvius volcanic complex were investigated by a multi-methodological approach including polarized optical microscopy, scanning electron microscope, electron microprobe analysis in wavelength-dispersive mode, laser ablation inductively coupled plasma mass spectroscopy, and single-crystal X‑ray diffraction. Five different groups of apatite, with different mineralogical and crystal-chemical features, were identified. Apatite crystals occur with well-developed hexagonal prismatic habit and, more rarely, with skeletal acicular forms. The crystals are yellow (type 1), transparent and colorless (type 2 and type 3), green (type 4) and aquamarine colored (type 5), with different paragenesis: macro-crystalline aggregates of clinopyroxenes, phlogopite, and apatite (type 1; type 4); clusters of apatite with micro-crystalline clinopyroxene, minerals of the cancrinite group, feldspars, and opaque minerals (type 2); aggregates of apatite, sellaite, wagnerite, gypsum, and phlogopite (type 3); aggregates of davyne, nepheline, mica group minerals, and apatite (type 5). Chemical analyses of apatites show variable amounts of Na, REE, Mg, Sr, and Fe replacing Ca, not negligible amounts of Si and S substituting P, and a significant substitution of Cl and OH instead of F. Five crystals representative of each apatite-type were studied by single-crystal X‑ray diffraction. Their crystal structure was refined in the hexagonal P6 3/m space group. A significant variation of the unit-cell parameters with the composition was observed. A comparative crystal-chemical analysis between apatites from Somma-Vesuvius and those from other localities is carried out.

Partially crystalline hornblende gabbro inclusions from the Little Glass Mountain Rhyolite contain euhedral plagioclase, orthopyroxene, hornblende, and apatite crystals in contact with interstitial rhyolitic (71-76% SiO 2 ) glass. Textural and mineral compositional data indicate that the gabbros crystallized sufficiently slowly that surface equilibrium was closely approached at the interface between crystals and the liquid. This rare occurrence represents a natural dynamic crystallization experiment with a “run time” that is not realistically achievable in the laboratory. SIMS analysis of mineral rim-glass pairs have permitted the determination of high-quality, equilibrium trace-element partition coefficients for all four minerals. These data augment the limited partition coefficient database for minerals in high-SiO 2 rhyolitic systems. For all minerals, the D values are consistent with those anticipated from crystal-chemical considerations. These data further support a liquid SiO 2 control on the REEs (and presumably other elements) partitioning wherein D values systematically increase with increasing liquid SiO 2 content.

In situ high- and low-temperature unpolarized FTIR absorption spectra of hydrous components in natural Fe-rich rutile have been recorded using a FTIR600 heating and cooling stage attached to an IR microscope. Two absorption bands (3279 and 3297 cm -1 ) at room temperature are ascribed to fundamental stretching bands of OH. Both OH bands shift to lower wavenumbers at elevated temperatures, but with different amplitudes. With increasing temperature, the integral absorbance of the 3279 cm -1 band increases while the integral absorbance of the 3297 cm -1 band decreases. These changes are fully reversible. The different frequency shifts of the two IR absorption bands with temperature imply two different local chemical environments of H defects. Based on the chemical composition of the rutile and the electronegativity of impurity ions, the results of the in situ high- and low-temperature FTIR measurements support the band assignment of Bromiley and Hilairet (2005): the 3279 and 3297 cm -1 bands are due to interstitial H decoupled from any substitutional defects, and H coupled to Fe 3+ on the neighboring octahedral (Ti) site (Fe 3+ Ti + H + i ↔ Ti 4+ Ti ), respectively. Variations in integral absorbance of the two bands suggest the transformation between decoupled H defects and coupled H defects as a function of temperature, possible due to some statistical relationship between the proportions of coupled and decoupled interstitial H dependent on the amount of heat energy applied to the system.

We evaluate analytical methods for characterizing hydrated and hydrous iron sulfate minerals (HHIS) that are typically metastable in air or vacuum, commonly form micrometer-sized particles, and contain multi-valent and light elements (Fe 2+ , Fe 3+ , OH − , and H 2 O) that may be challenging to quantify. We synthesized or obtained HHIS-szomolnokite, melanterite, rhomboclase, schwertmannite, ferricopiapite, paracoquimbite, and jarosite-as well as Fe-oxides. These nominally pure samples were characterized with X‑ray diffraction (XRD), and then used to evaluate bulk analyses obtained from combined inductively coupled plasma, optical emission spectroscopy (ICP-OES), ion chromatography (IC), Mössbauer spectroscopy, and mass spectrometry. Integrated bulk analyses showed excellent agreement with the nominal formulas for the minerals. Because HHIS commonly form micro-sized particles-for example, HHIS found in acid mine drainage (AMD) environments and in martian meteorites-it is necessary to develop micro-analytical techniques. Microscopic mid-infrared spectroscopy allows the analyst to successfully discriminate among HHIS with minimal sample preparation on the small scale (-40 × 40 μm). For chemical analysis, electron probe microanalysis (EPMA) is preferred for samples that can be mounted, polished, coated, and that are stable under high vacuum; however, few HHIS meet those criteria. To characterize HHIS compositions, we show that multiple low-vacuum scanning electron microscopy (SEM) analyses of the same uncoated, unpolished mineral are required. Analysis of each mineral shows linear trends on ternary diagrams of 5×Fe-SO4-O (where oxygen is in O, OH, and H 2 O) that may be used to narrow down the HHIS mineralogy. Low-vacuum SEM also provides invaluable information about the geochemical and textural context of the samples. Our study provides protocols for microanalysis of these challenging, fine-grained, and metastable HHIS that may also be applied to other mineral groups.

The crystal chemistry of Ti-rich ferriallanite-(Ce) in syenites from Cape Ashizuri, Shikoku Island, Japan, was studied using electron microprobe analysis (EMPA) and single-crystal X‑ray diffraction methods. Our specimens (AS001 and AS304) are characterized by high-Ti (-3.6 wt% TiO 2 ) and Fe contents (-21.3 wt% FeO*; Fe 2+ /total Fe = 0.6-0.7). Structure refinements of two ferriallanite-(Ce) crystals converged to R1 = 1.50-1.57%. In both specimens, the dominant cations at A1, A2, and M3 are Ca, Ce, and Fe 2+ , respectively. However, depending on Ti assignment, two different schemes of the cation distributions at M1 and M2 can be considered: (1) (Fe 0.72 Ti 0.23 Al 0.05 )M1(Al 0.82 Fe 3+ 0.18 )M2 and (2) (Fe 0.90 Al 0.10 )M1(Al 0.77 Ti 0.23 )M2 for AS001, and (1) (Fe 0.65 Ti 0.29 Al 0.06 )M1(Al 0.89 Fe 3+ 0.11 )M2 and (2) (Fe 0.76 Ti 0.13 Al 0.11 )M1(Al 0.84 Ti 0.16 )M2 for AS304. The Si 2 O 7 group is compressed along Sil-O9-Si2 direction because of the expansions of the M1O6 and M3O6 octahedra due to substitution of large octahedral cations for Al. This compression is monitored by the atom position of O9 that shifts away from the cation at A1 decreasing the Si1-O9-Si2 angle. In allanite-subgroup minerals, the A1-O9 distance is longer and the bridging angle is smaller than those of clinozoisite-subgroup minerals. Although the A1 polyhedron is generally described as a ninefold-coordinated site, it is appropriately described as sevenfold-coordinated in Ti-rich allanite-(Ce) because of the lengthened A1-O9 (×2) distance. The cation substitutions at M1 and M3 indirectly affect the topology of the A1 polyhedron.

The transformation of pyrrhotite to Fe disulfide (pyrite and/or marcasite) under hydrothermal conditions was studied experimentally by probing the effects of temperature (up to 220 °C, vaporsaturated pressures), ΣS(-II) concentrations, pH, and availability of oxygen on reaction progress and on the resulting textures. The pyrrhotite to Fe disulfide reaction proceeded by a dissolution-reprecipitation mechanism under all conditions. Marcasite and pyrite formed under both oxic and anaerobic conditions, which is inconsistent with the traditionally assumed polysulfide route for FeS 2 formation (oxidants required for polysulfide formation). The nature of the products was controlled by the level of supersaturation of the solution with respect to Fe disulfide minerals. Marcasite formed preferentially at low pH or S(-II)-deficient solutions (saturation index << 1000), while pyrite was the main product at saturation indices >1000. Different textures were obtained for the replacement of pyrrhotite by either pyrite or marcasite. Pyrite formation proceeded by direct replacement of pyrrhotite and, simultaneously, by overgrowth from solution. The pyrite crystals were >10 μm in size and randomly oriented. In comparison, marcasite crystals were <1 μm in size, and no significant overgrowth was observed. At pH 21°C <3, the marcasite nanocrystals showed the well-known crystallographic relationship with pyrrhotite, but at pH 21°C 3.96, the marcasite crystallites were randomly oriented. These experimental results confirm that the preservation of the crystallographic orientation is not a distinguishing feature between dissolution-reprecipitation and solid-state reactions. The different textures among pyrite and marcasite reflect the dominance of crystal growth (pyrite) vs. nucleation (marcasite) as a precipitation mechanism.

Argandite, Mn 7 (VO 4 ) 2 (OH) 8 , is a new mineral from the metamorphosed synsedimentary exhalative Mn deposit located underneath the Pipji glacier (Pipjigletscher) in the Turtmann valley, Central Alps, Switzerland. The mineral is dedicated to the Swiss geologist Émile Argand (1879-1940). Argandite occurs in manganosite-rich ores in association with the V-minerals pyrobelonite, reppiaite, and an unknown silico-vanadate with chemical formula (Mn,Mg) 24 (V,As,Si) 4 Si 2 O 27 H 38 ; these minerals result from the remobilization of ore components during the Tertiary Alpine metamorphism under upper greenschist facies conditions (-450 °C, 4-6 kbar). Argandite forms isolated anhedral grains up to 60 μm in diameter. The mineral is transparent, orange in color with a pale orange streak and vitreous luster, Mohs hardness -3.5-4, Dcalc 3.67(1), and Dmeas 3.71(5) g/cm 3 . It is brittle with one distinct cleavage, probably parallel to {001}. Argandite is biaxial negative, with α -1.74, β = 1.762(4), γ -1.77 (white light), 2V (calc) = -62°. It shows a distinct pleochroism under polarized light, orange-yellow to orange. The empirical chemical formula is (Mn 6.54 Mg 0.38 Ni 0.04 Ca 0.02 Zn 0.01 Sr 0.01 ) Σ=7.00 (V 1.46 ,As 0.54 ) Σ=2.00 O 8 (OH) 8.00. Argandite is monoclinic, space group P21/n, a = 5.5038(2), b = 12.2665(5), c = 10.1055(5) Å, β = 95.559(4)°; V = 679.04(5) Å 3 ; Z = 2. The six strongest lines measured in the X‑ray powder diffraction pattern are [d in Å (I)(hkl)]: 3.074 (100)(131), 2.687 (70)(140;113), 3.395 (60)(112), 3.708 (50) (112;121), 2.945 (50)(041;113), and 2.522 (50)(004;202). The crystal structure was solved with direct methods on the basis of 1661 unique reflections with I > 4σF and refined to R1 = 3.40%. Argandite is isostructural with allactite, Mn 7 (AsO 4 ) 2 (OH) 8 , and raadeite, Mn 7 (PO 4 ) 2 (OH) 8 .

Murchisite (IMA 2010-003), Cr 5 S 6 , is a new chromium sulfide mineral, discovered in the Murchison CM2 meteorite. The type material occurs as one subhedral crystal (1.3 × 4 mm in size) in contact with low-Ni iron (“kamacite”), martensitic iron, schreibersite, and a Ca-,Al-rich glass, all of which are included in an isolated forsteritic olivine grain in the meteorite’s matrix. The mean chemical composition determined by electron microprobe analysis of the type material is (wt%) Cr 53.32, S 42.87, V 1.44, Fe 1.14, P 0.10, Ni 0.10, sum 98.97. The empirical formula calculated on the basis of 6 S atoms is (Cr 4.60 V 0.13 Fe 0.09 Ni 0.01 ) Σ4.83 (S 6.00 P 0.01 ) Σ6.01 . Murchisite was also identified in another isolated olivine grain from the same meteorite. These crystals are subhedral to round in shape, 300 nm to 1 mm in size, and occur in association with tochilinite and serpentine, within which it is included, chromite, and eskolaite. Its electron backscatter diffraction patterns are an excellent match to that of synthetic Cr 5 S 6 with the P31c structure, showing a = 5.982, c = 11.509 Å, V = 356.67 Å 3 , and Z = 2, based on previously published data from synthetic material. Murchisite is named for the locality (the Murchison meteorite). It is a low-temperature phase (~327 °C in the Cr-S system), probably formed from higher temperature Cr 1-x S exsolved or expelled from a Cr-,S-bearing, metal-rich spherule included in forsteritic olivine grains that were probably derived from chondrule fragments. The formation of this phase reflects sulfur fugacities intermediate between those that would have led to troilite and those that would have led to no sulfide at all. The high-temperature Cr 1-x S phase equilibrated with coexisting alloys to ~600 °C. Murchisite formed from this precursor at low temperatures (<~300 °C) through ordering of S vacancies.