Volume 92, Issue 10

We report evidence for high ferric iron to total iron (Fe 3+ /ΣFe) ratios in Al-bearing akimotoite coexisting with other high-pressure silicates and Fe-Ni metal from shock melt-veins in the Sixiangkou (L-6) chondrite. The measurements were made using electron energy-loss near-edge structure (ELNES) spectroscopy. The results demonstrate that akimotoite in shock-melt veins of this meteorite has high proportions of Fe 3+ , with a Fe 3+ /ΣFe ratio of 0.67(3). In contrast, the coexisting majoritic garnet and ringwoodite, which are the typical Fe-bearing phases in shock veins in this meteorite, are enriched in Fe 2+ rather than Fe 3+ , with Fe 3+ /ΣFe ratios of 0.10(5) and 0.15(5), respectively. We conclude that the higher affinity of Fe 3+ for akimotoite, rather than for the other dense silicate phases, is related strongly to the substitution mechanism of trivalent cations. This mechanism is described as VI(A) Fe 3+ + VI(B) Al 3+ = VI(A) Mg 2+ + VI(B) Si 4+ in the ABO 3 structural formula of MgSiO 3 -ilmenite under high pressures and temperatures, and operates even at a low oxygen fugacity where Fe-Ni metal is stable.

The microstructures of two-phase binary aggregates of ice-I + salt-hydrate, prepared by eutectic solidification, have been characterized by cryogenic scanning electron microscopy (CSEM). The specific binary systems studied were H 2 O-Na 2 SO 4 , H 2 O-MgSO 4 , H 2 O-NaCl, and H 2 O-H 2 SO 4 ; these were selected based on their potential application to the study of tectonics on the Jovian moon Europa. Homogeneous liquid solutions of eutectic compositions were undercooled modestly (ΔT ~ 1.5 °C); similarly cooled crystalline seeds of the same composition were added to circumvent the thermodynamic barrier to nucleation and to control eutectic growth under (approximately) isothermal conditions. CSEM revealed classic eutectic solidification microstructures with the hydrate phase forming continuous lamellae, discontinuous lamellae, or forming the matrix around rods of ice-I, depending on the volume fractions of the phases and their entropy of dissolving and forming a homogeneous aqueous solution. We quantify aspects of the solidification behavior and microstructures for each system and, with these data, articulate anticipated effects of the microstructure on the mechanical responses of the materials.

A quartz-monazite oxygen isotope thermometer was calibrated based on δ 18 O measurements of mineral separates from monazite-bearing rocks and on piston cylinder calcite-monazite oxygen exchange experiments. The oxygen isotope composition of monazite was measured using secondary ion mass spectrometry (SIMS) and multiple fluorination techniques. The results of these measurements suggest that (1) differences in Th content of monazite can cause the instrumental mass fractionation in an ion microprobe to vary by at least 4‰; (2) the oxygen isotope compositions of chemically distinct zones in the monazite grains analyzed are probably similar; and (3) δ 18 O mnz is most accurately determined by extracting oxygen via fluorination in nickel vessels. Comparing the oxygen isotope fractionation between quartz and monazite with independently derived temperature estimates suggests that (1) the coefficient of fractionation between quartz and monazite (a qtz-mnz ) equals 2.2 ± 0.6, and (2) ~100 μm monazite grains in a multiply metamorphosed, granulite facies orthogneiss from the Wind River Range record the high-temperature history of this rock, whereas other isotopic thermometers suffered retrograde oxygen exchange. This evidence indicates that monazite might be used to constrain peak metamorphic temperatures, which may correlate with the ages recorded by the same mineral.

Experimental brackets on the melting temperature of high albite (NaAlSi 3 O 8 ) were determined at 2.33 ± 0.03 GPa (1360-1370 °C) and 2.79 ± 0.03 GPa (1370-1389 °C) in a piston-cylinder apparatus. All run products that quenched to a glass were analyzed by Fourier-transform infrared spectroscopy and found to contain ≤500 ppm H 2 O. In addition, new X-ray diffraction experiments on fully disordered albite are reported to 7.6 GPa; the fitted results lead to a zero-pressure bulk modulus (K 0 ) of 56.4 ± 0.7 and a pressure derivative (K 0 ′) of 3.9 ± 0.3 in a third-order Birch-Murnaghan equation of state. Revised values for the enthalpy and entropy of fusion of high albite at one bar and 1100 °C [Δ HTf = 64.5 ± 2.1 kJ/mol and Δ STf = 47.0 J/(mol·K)] are recommended on the basis of improved heat capacity equations for NaAlSi 3 O 8 glass and liquid. On the basis of these new results on the fusion curve and thermodynamic data for high albite, the pressure dependence of the NaAlSi 3 O 8 liquid compressibility (K 0 ′) is constrained to be 10.8 ± 1.5 in a third-order Birch-Murnaghan equation of state. The uncertainty in K 0 ′ of ±1.5 contributes an error to melt density at 3 GPa (2.543 ± 0.010 g/cm3 at 1500 °C) of ±0.4%.

The stacking structures of sudoite, di-trioctahedral chlorite from two different localities are investigated by powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD analyses using a Gandolfi camera revealed that the structures of both specimens are similar, corresponding to a one-layer IIbb-4 (1A) polytype. HRTEM observations indicate that the stacking sequence is characterized by a largely uniform intralayer shift of a/3 in the -X 1 direction (X i represent the directions along the pseudohexagonal axes) and by an interlayer displacement of similar magnitude in either the -X 2 or -X 3 direction. Stacking disorder is primarily caused by the mixing of interlayer displacements in the two directions. This disorder is more common in the lath-shaped crystalline specimen from Berezovsk, Russia than in the fine platy crystalline specimen from Ottré, Belgium. DIFFaX simulations of the powder XRD patterns for this stacking model reproduced the observed features well for both specimens. The stacking configuration of these sudoite specimens is considered to be controlled by the corrugation of basal oxygen planes in the 2:1 layer and the corresponding deformation in the brucite-like interlayer sheet.

The vibrational spectra of H-substituted forsterite (MgSiO 4 H 2 ) in which the Mg 2+ at the M1 or M2 site is replaced by two H ions have been investigated by first-principles molecular dynamics calculations. Infrared spectra have been obtained and assigned with the aid of atomic vibrational density of states and the analysis of the atom radial distribution functions. It is shown that the proton dynamics are different at the M1 and M2 site. In the latter case, the proton does not remain bound to a single O atom but hops between O atoms in close proximity. This fluxional motion is highly temperature dependent. These fluxional motions results in substantially lower energy O-H stretching vibrations spanning a broad frequency range from 2000 to 3000 cm -1 . The present results will be useful for the characterization of the IR spectrum of H + -substituted (leached) olivine under ambient conditions.

Fluorophlogopite, a new F-dominant mineral of the mica group, was found at Monte Calvario, Biancavilla, lower southwestern flanks of Mt. Etna volcano (Catania, Sicily, Italy). The mineral occurs in autoclasts of gray-red altered benmoreitic lavas, primarily associated with fluoro-edenite, alkali-feldspars, clino- and ortho-pyroxenes, fluorapatite, hematite, and pseudobrookite. It was formed by metasomatism of the original lava rocks from very hot fluid enriched in F, Cl, and other incompatible elements. Fluorophlogopite occurs as very thin laminae with a diameter of 200 to 400 μm. Main physical properties are pale yellow in color; yellowish-white in thin section; vitreous to resinous luster; transparent; non-fluorescent; Mohs’ hardness 2-3; brittle and malleable; perfect cleavage on {001}; biaxial (-), α calc = 1.5430(8), β = 1.5682(5), γ = 1.5688(5) (λ = 589 nm); 2V meas = 17(2)°; α = acute bisectrix ⊥ (001); nonpleochroic; D calc = 2.830 g/cm 3 (using empirical formula and single-crystal unit-cell parameters), D calc = 2.842 g/cm 3 (using empirical formula and powder cell constants). Infrared spectrum did not show a significant absorption band in the OH-stretching region (3800-3600 cm -1 ) confirming that the F content of the fluorophlogopite from Biancavilla is close to the stoichiometric value. Unit-cell parameters from X-ray powder-diffraction data (114.6 mm diameter Gandolfi camera, CuKα) are a = 5.305(2), b = 9.189(3), c = 10.137(4) Å, β = 100.02(3)°. These data agree with those obtained by single-crystal X-ray studies on a very thin (~15 μm) fluorophlogopite crystal, i.e., Monoclinic (1M polytype); Space Group C2/m; a = 5.3094(4), b = 9.1933(7), c = 10.1437(8) Å, β = 100.062(5)°, V = 487.51(6) Å 3 , Z = 2. Structure refinements using anisotropic displacement parameters converged at R = 3.50, Rw = 4.37, R sym = 3.72%. Electron microprobe analysis performed on the same crystal used for X-ray investigation gave: SiO 2 = 45.75(39), TiO 2 = 1.05(5), Al 2 O 3 = 9.60(19), MgO = 27.92(30), MnO = 0.16(3), FeO tot = 1.25(6), BaO = 0.09(5), K 2 O = 8.22(11), Na 2 O = 0.61(30), Cl = 0.02(1) wt%. Secondary Ion Mass Spectrometry (SIMS) was used to estimate light elements [Li 2 O = 0.30(1) and H 2 O = 0.16(2) wt%] and fluorine content [F = 8.69(24) wt%]. The new mineral fluorophlogopite and its name were approved by IMA-CNMMN (2006/011).

The structural behavior of thomsonite compressed in aqueous medium up to 3 GPa was studied by means of in situ synchrotron powder diffraction with a diamond anvil cell. In the range between 0.0001 and 2 GPa, the compressibility of thomsonite is markedly lower than that reported previously, where a non-penetrating medium (with only 6% H 2 O) was used. This indicates a pressure-induced hydration (PIH), which results in the transition to an over-hydrated phase observed at 2 GPa. The structure of over-hydrated thomsonite contains one additional, half-occupied H 2 O position, coordinated by the calcium at the Ca2 site, with a scolecite-like coordination [CaO 4 (H 2 O) 3 ]. The appearance of new H 2 O position causes a 4.5% volume expansion through the cooperative rotation of [T 2 O 5 ] ∞ chains, leading to the enlargement of the cross-section of the main channels parallel to c axis. The observed deformation mechanism is similar to that found in high-hydrated and super-hydrated natrolite, although only a half of the channels are affected by PIH. The present data indicate that the over-hydration effect in fibrous zeolites strongly depends on the partial water pressure in compressing medium.

The pressure-induced behavior of spin-allowed dd-bands of VIII Co 2+ in the absorption spectra of synthetic Co 3 Al 2 Si 3 O 12 garnet was studied from 10 -4 to 13 GPa. The plots of the peak energy vs. pressure for the three sharpest well resolved bands at ca. 5160, 17 680, and 18 740 cm -1 display small but discernible breaks in linear relations between 4 and 5 GPa. Data from single-crystal X-ray diffraction likewise show discontinuities in trends of CoO 8 polyhedral volume and distortion, and Co-O and Si-O bond distances over this pressure range. These effects are related to a pressure-induced phase transition from the β- to α-isostructural polymorph of Co 3 Al 2 Si 3 O 12 .

In situ observations of the decomposition of kyanite, Al 2 SiO 5 , were carried out in a multi-anvil high-pressure apparatus using synchrotron radiation, where the phase change from kyanite to stishovite + corundum was observed at high pressures and high temperatures. The phase boundary of this decomposition at T = 1200-1900 K and P = 5-15 GPa was determined to be, P (GPa) = 10.2 + 0.0016 × T (K). Previous studies using the quench method showed a discrepancy in the transition pressure of the decomposition. Our results using in-situ observations resolve this dispute.

Bouazzerite, Bi 6 (Mg,Co) 11 Fe 14 [AsO 4 ] 18 O 12 (OH) 4 (H 2 O) 86 , is a new mineral occurring in “Filon 7” at the Bou Azzer mine, Anti-Atlas, Morocco. Bouazzerite is associated with quartz, chalcopyrite, native gold, erythrite, talmessite/roselite-beta, Cr-bearing yukonite, alumopharmacosiderite, powellite, and a blue-green earthy copper arsenate related to geminite. The mineral results from the weathering of a Variscan hydrothermal As-Co-Ni-Ag-Au vein. The Bou Azzer mine and the similarly named district have produced many outstanding mineral specimens, including the world’s best erythrite and roselite. Bouazzerite forms monoclinic prismatic {021} crystals up to 0.5 mm in length. It has a pale apple green color, a colorless streak, and is translucent with adamantine luster. d calc is 2.81(2) g/cm 3 (from X-ray structure refi nement). The new mineral is biaxial with very weak pleochroism from yellow to pale yellow; the refractive indices measured on the (021) cleavage face range from n min = 1.657 to n max = 1.660; the Gladstone-Dale relationship provides a value of 1.65. The empirical chemical formula is Bi 6.14 Fe 12.6 Mg 8.45 Co 0.48 Ni 0.12 Ca 0.23 (As 17.0 Cr 0.64 Si 0.32 ) Σ=18.0 O 174.6 H 184 . Bouazzerite is monoclinic, P2 1 /n, Z = 2, with a = 13.6322(13) Å, b = 30.469(3) Å, c = 18.4671(18) Å, β = 91.134(2)°, and V = 7669.0(13) Å 3 . The eight strongest lines in the X-ray powder diffraction pattern are [d in Å (I)(hkl)]: 11.79(100)(021̅), 10.98(80)(101/1̅01), 10.16(80)(1̅20), 7.900(80)(022̅), 12.45(70)(11̅0), 15.78(60)(01̅1), 3.414(40)(333/400), 3.153(40)(353/22̅5). The crystal structure of bouazzerite is based upon [Bi 3 Fe 7 O 6 (OH) 2 (AsO 4 ) 9 ] 11- anionic nanoclusters that are built around [ trigonal prismatic Fe 3+ ( octahedral Fe 3+ 3 (OH)O 12 ) 2 ] 29- groups, containing one Fe 3+ ion in trigonal prismatic coordination and six Fe 3+ ions in octahedral coordination. The nanoclusters have a diameter of about 1.3 nm and are linked together by chains of Mg(O,H 2 O) 6 octahedra. The resulting arrangement displays channels down [100] that contain structural water. Bouazzerite is the fi rst mineral based upon Bi- and As-containing ferric nanoclusters. Its discovery provides a unique insight into transport mechanisms of toxic elements in the oxidation zones of sulfi de mineral deposits in the form of complex Fe-As nanoparticles.

The crystal structure of diaspore, AlO(OH), has been investigated by in situ single-crystal synchrotron X-ray diffraction at ~50 GPa using the diamond-anvil cell technique. Diaspore is found to retain its structure up to 51.5 GPa at room temperature, which is more than 30 GPa above the transition pressure to δ-AlO(OH) found in quenched high-temperature experiments and derived from density functional theory calculations. The compression is anisotropic and largest for the a axis. This can be explained by the fact that the structural response to pressure is mainly due to the shortening of the hydrogen bond, which is oriented nearly parallel to the a axis. The hydrogen bond becomes significantly more symmetric with pressure up to 50 GPa.

This paper reports a single-crystal unpolarized-light FTIR study in the OH-stretching region of a suite of well-characterized Ti-rich pargasites from Lherz (French Pyrenees). All amphiboles studied have fairly constant M-site composition, with [6] Al tot ~0.55 atoms per formula unit (apfu), [6] Ti ~0.45 apfu, and [6] Fe 3+ ~0.40 apfu. SIMS and SREF data show all samples to have an O3 anion composition of OH ≈ O 2- ≈ 1.0 apfu, with negligible F. The FTIR spectra show for all samples a broad absorption consisting of several overlapping bands; three main components can be recognized: ~3710, 3686, and 3660 cm -1 , respectively, with an asymmetric tail extending to lower frequency. Six Gaussian components can be fitted to the spectra; comparison with spectra of both synthetic and natural pargasites allows five of these components to be assigned to local configurations involving OH-O 2- at the O3 site, thus showing that coupling with an O 2- anion through an A-cation significantly affects band position. Infrared spectroscopy can detect the presence of O 2- in amphiboles in chemically favorable cases, i.e., in the absence of F. Moreover, the FTIR spectra show that all octahedral configurations involving M1 Ti 4+ or M1 Fe 3+ M3 Fe 3+ are associated with O 2- at both adjacent O3 sites, and that M3 Al is locally associated with OH, confirming SRO models based on structure refinement results.

Monazite is both partially replaced and overgrown by a ThSiO 4 phase along grain rims in a series of experiments from 300 to 900 °C and 200 to 1000 MPa. All experiments consisted of 10 mg of 100.500 μm size, euhedral to subhedral crystals of a natural Th-free monazite-(Ce), 5 mg of Th(NO 3 ) 4 ·5H 2 O, 2.5 mg of SiO 2 , and 5 mg of H 2 O loaded into 3 mm wide, 1 or 1.3 cm long platinum capsules that were arc welded shut. Experimental conditions were: 300 °C at 200 and 500 MPa; 300, 400, 500, 600, and 700 °C at 500 MPa (cold seal hydrothermal autoclave); and 900 °C at 1000 MPa (Catz assembly; pistoncylinder press). Back-scattered electron (BSE) imaging, electron back-scattered diffraction (EBSD) analysis, and transmission electron microscopy (TEM) indicates that in the experiments from 500 to 900 °C, the ThSiO 4 phase took the form of monoclinic huttonite implying that huttonite, associated with monazite, could exist metastably over a much greater P-T range than previously thought. TEM analysis of a foil cut perpendicular to the monazite-huttonite interface from the 600 °C, 500 MPa experiment using a focused ion beam (FIB) indicates that the huttonite as well as the interface between the huttonite and monazite is characterized by fluid inclusions. High-resolution TEM analysis indicates that the huttonite-monazite interface is coherent. In the case of replacement of monazite by huttonite, fluid-aided dissolution-reprecipitation is proposed as the most likely mechanism responsible.

Resonant ultrasound spectra of a single crystal and a polycrystalline sample of lawsonite [CaAl 2 Si 2 O 2 (OH) 2 ·H 2 O] have been measured at room temperature and at low temperatures in the region 20-300 K. The influence of known phase transitions at 125 and 270 K is seen in the frequency variations of the resonance peaks, which are indicative of elastic stiffening, and in values for the quality factor Q QF , which are indicative of dissipation. Two dissipation peaks, at ~250 and ~210 K, are interpreted as being due to the proton order-disorder processes associated with the two species of hydrogen atoms in the structure: one in hydroxyl OH groups and one in the H 2 O molecules. These occur below the Cmcm ↔ Pmcn transition point but coincide with changes in the shear elastic constants and in features of IR spectra reported elsewhere. A third, much smaller, dissipation peak occurs immediately below the Pmcn ↔ P2 1 cn transition point. The combination of these anomalies in acoustic dissipation and in elastic constants is consistent with the view that the Cmcm ↔ Pmcn transition is driven both by displacive and proton ordering effects. For the Pmcn ↔ P2 1 cn transition, dissipation and the transition are more closely related, consistent with the view that the transition is driven essentially by proton ordering.

The relationship between magnetic properties and chemical composition of 19 natural carbonate single crystals of the calcite, aragonite, and dolomite groups and of azurite were investigated. Magnetic susceptibility was determined in low fields, and magnetic anisotropy was measured at room temperature and at 77 K using a high-field torque magnetometer. The chemical composition was analyzed using LA-ICP MS. Planar arrangement of the CO 3 -groups generates an oblate diamagnetic anisotropy with the minimum susceptibility k 3 along the crystallographic c-axis in all investigated anhydrous carbonate minerals. A prolate paramagnetic anisotropy with the maximum susceptibility k 1 along the c-axis is produced by Fe 2+ in the trigonal carbonate lattice, which can lead to a transition from oblate to prolate shape of the total anisotropy. The transition occurs in the calcite structure above an Fe concentration of 400 ppm at room temperature and 150 ppm at 77 K. The susceptibility difference k 1 - k 3 for pure calcite is 4.06 × 10 -10 m 3 /kg and increases to 9.4 × 10 -9 m 3 /kg for 10 800 ppm Fe. In the hexagonal aragonite structure, no paramagnetic anisotropy due to Fe 2+ was detected. Azurite shows a strong anisotropy with k 1 - k 3 = 1.5 × 10 -8 m 3 /kg, which is assigned to Cu 2+ . The paramagnetic anisotropy due to Fe 2+ increases at 77 K in minerals of the calcite and dolomite group and in azurite, but not in minerals of the aragonite group. Upon cooling from room temperature to 77 K, k 1 - k 3 increases 13.3 times for 500 ppm to 100 000 ppm Fe 2+ in the trigonal lattice and 7.2 times for siderite.

This paper reports a structure analysis of the åkermanite-gehlenite solid solution. This solution is non-ideal with a negative excess volume in the entire compositional range. X-ray diffraction shows anomalous behavior of the cell parameters close to the gehlenite end-member (åk 08 ge 92 , åk 35 ge 65 ). This behavior is correlated with an excess of Si and deficiency of Al with respect to the Mg content, which implies a defective, non-stoichiometric structure with Ca vacancies. Electron microscopy images have confirmed an increase in the defectivity on the atomic scale for Al-rich compositions, and single-crystal structure refinements show a correlated decrease of the tetrahedral volume preferentially occupied by Si. The incommensurate modulation, characteristic of åkermanite, has been observed also in åk 95 ge 05 , and it is still visible as diffuse scattering in åk 75 ge 25 . (210) twinning has been observed in the entire compositional range.

The system Al 2 O 3 -P 2 O 5 -H 2 O contains many phosphate minerals that occur in various geologic environments. The natural occurrence of variscite (AlPO 4 ·2H 2 O, orthorhombic), including its monoclinic polymorph metavariscite, is largely restricted to soils and aluminous rocks like Al-rich igneous rocks and shales, which interacted with P-rich hydrothermal solutions or groundwater. Variscite dehydrates to berlinite (AlPO 4 ) and a hydrous P-Al-rich fluid. This dehydration reaction AlPO 4 ·2H 2 O = AlPO 4 + 2H 2 O is, however, metastable, at low concentrations of P in the fluid, because berlinite breaks down at lower temperature to augelite [Al 4 PO 4 (OH) 3 ] + H 3 PO 4 + H 2 O and trolleite [Al 4 (PO 4 ) 3 (OH) 3 ] + H 3 PO 4 + H 2 O. The variscite/metavariscite = berlinite equilibrium has been investigated by synthesis experiments from mixtures of γ-Al 2 O 3 and excess phosphoric acid at pressures between 1 and 5 kbar and temperatures of 100-200 °C using standard cold-seal vessels. The hydration-dehydration equilibrium is mainly controlled by temperature and only weakly by pressure. At 4 and 5 kbar, variscite/metavariscite were found at temperatures of ~150 °C, at lower pressure at 115-125 °C in accordance with their natural mode of occurrence. In this T range, however, variscite/metavariscite is not the sole phase but is always accompanied by variable but generally minor amounts of wavellite and trolleite Al 4 (PO 4 ) 3 (OH) 3 . Secondary wavellite Al 3 (PO 4 ) 2 (OH) 3 ·5H 2 O, hydrated Al-phosphate AlPO 4 ·xH 2 O (1.1 ≤ x ≤ 1.3) and Al-metaphosphate hexahydrate Al(H 2 PO 4 ) 3 formed during quenching and/or drying of the runs. Berlinite is the reaction product at temperatures 200 °C/4-5 kbar and 150 °C/1-3 kbar and may be associated with augelite and trolleite.

Chrysotile from Thetford, Quebec, was heated at constant temperature in quench furnaces from 200 to 1000 °C for 4 to 720 h, and the products were analyzed by XRD and optical microscopy. XRD patterns for chrysotile from Thedford, Jeffrey Quebec, and New Idria, California, heated for up to 8 h at constant temperatures from 400 to 800 °C in hydrothermal diamond-anvil cells, were obtained at 300 s intervals by using synchrotron radiation. The studies show that differences in the decomposition temperatures of chrysotile reported in the literature can be explained by differences in the temperatures, time at temperature, particle size, and partial pressure of water. Chrysotile heated for 30 days is destroyed between 475 and 500 °C, whereas chrysotile heated to 800 °C survives for only minutes. A prograde heating experiment, consistent with the literature, shows chrysotile destruction beginning at 600 °C and completed at 750 °C, demonstrating that such experiments should not be used to establish temperatures of thermal stability. Forsterite forms readily at 600 °C when water is retained transiently in the decomposition products, but does not form after 4 h of heating samples of small fiber size and high surface area from which water is readily lost. When water is retained in the sample chamber during heating to 800 °C over 4 h, a rapid destruction of chrysotile and formation of forsterite was observed, followed by the appearance and later destruction of the intermediate reaction products talc, a tridymite-like phase, and anthophyllite; enstatite appearance coincides with the destruction of the tridymite-like phase and talc. In quench experiments, a 10+ Å phase is observed between 500 and 600 °C, and talc is observed between 587 and 800 °C. The optical properties of the run products between 600 and 900 °C are highly variable, with a range in the index of refraction perpendicular to length of up to 0.06 and a minimum index of refraction 0.03 below the starting material in fibers in the 650 °C run product; the variability reflects the inhomogeneity in products and reactants in this temperature range. In quench experiments, the intensity of the XRD patterns of chrysotile decreased on heating between 200 and 400 °C, and increased at 450 °C, demonstrating recrystallization of chrysotile. A gradual heating experiment showed a similar pattern with the lowest intensities at 250 °C and maximum intensities at 550 °C. The two types of chrysotile reported in the literature may reflect simply the presence of chrysotile of different particle sizes. Chrysotile may also possess a spectrum of stabilities due to variable strain energies of curvature. The presence of a tridymite-like phase supports the formation of a Si-rich dehydroxylate II. The absence of forsterite and chrysotile in brake-wear debris reflects the high temperature and disaggregated fiber bundles resulting from friction.

Thermodynamic calculations of ion-exchange reactions were applied for clinoptilolite in a natural state and after irradiation with three doses of β-radiation (10 12 , 10 15 , 3 × 10 16 e/cm 2 ) and γ-radiation (70 Mrad). Samples were equilibrated with binary systems of K + ↔ Na + and Cs + ↔ Na + at 25° and a total normality of 0.025 N. Selectivity for K was not affected after β-radiation with doses of 1012 and 1015 e/cm 2 (ΔG° = -6.37 kJ/equiv, lnKα = 2.58 for the original clinoptilolite), whereas it increased considerably after 70 Mrad of γ-radiation (ΔG° = -7.88 kJ/equiv, lnKα = 3.18). Selectivity for Cs + increased for the clinoptilolite irradiated with β-radiation (10 12 , 10 15 , 3 × 10 16 e/cm 2 ) and γ-radiation (70 Mrad). ΔG° and lnKα for original sample and Cs + ↔ Na + were -7.33 kJ/equiv and 2.96, respectively. Irradiated samples with β-radiation 10 12 , 10 15 , 3 × 10 16 e/cm 2 and 70 Mrad γ-radiation yielded ΔG° and lnKα -7.41, -8.83, -8.60, -8.25 kJ/equiv and 2.99, 3.57, 3.47, 3.33 for Cs + ↔ Na + , respectively. Remarkable amorphization of clinoptilolite was observed after exposure at the highest dose of β-radiation (3 × 10 16 e/cm 2 ) with a concomitant decrease in cation-exchange capacity (CEC). Crystallographic parameters and especially exchangeable cation site coordinates were refined for all samples with the Rietveld method. Cesium-saturated samples exhibited changes in the cation sites Cs 2 and Cs 3 , which are next to clinoptilolite channel walls with lower Al 3+ for Si 4+ substitution. The observed changes include a shift in cation sites Cs2 and Cs3 toward channel walls and occupancy decrease in site Cs2.

Hydration of the <1 μm size fraction of a high-charge montmorillonite (Clay Minerals Society Source Clay SAz-1), and of low- and high-charge beidellites (Source Clays SbId-1 and SbCa-1, respectively) was studied by modeling of X-ray diffraction patterns recorded under controlled relative humidity (RH) for Sr- and/or Ca-saturated specimens. The influence of layer charge and charge location on smectite hydration was studied. Distribution of layers with different hydration states (dehydrated-0W, monohydrated-1W, bihydrated-2W, or tri-hydrated-3W) within smectite crystals often leads to two distinct contributions to the X-ray diffraction pattern, each contribution having different layer types randomly interstratified. Structure models are more heterogeneous for beidellite than for montmorillonite. For beidellite, two distinct populations of particles with different coherent scattering domain sizes account for the heterogeneity. Increased hydration heterogeneity in beidellite originates also from the presence of 0W (non-expandable) and of 1W layers under high relative humidity (RH) conditions. Similarly, after ethylene-glycol (EG) solvation, some beidellite layers incorporate only one plane of EG molecules whereas homogeneous swelling was observed for montmorillonite with the systematic presence of two planes of EG molecules. For montmorillonite and beidellite, the increase of layer charge shifts the 2W-to-1W and the 1Wto- 0W transitions toward lower RH values. For all samples, layer thickness of 0, 1, and 2W layer types was similar to that determined for low-charge SWy-1 montmorillonite (Source Clay SWy-1), and no change of layer thickness was observed as a function of the amount or of the location of layer charge. However, layer thickness increased with increasing RH conditions.

Large single crystals of MgSiO 3 perovskite were successfully synthesized by a thermal gradient method at 24 GPa and 1500 °C. This was achieved by an improvement of high-pressure synthesis technique that allowed us to grow single crystals under such ultrahigh-pressure conditions in relatively large volumes (e.g., 10 mm 3 ). Since crystal growth is hindered by neighboring crystals, the nucleation density was suppressed by reducing the thermal gradient to 20 °C/mm, permitting an increase in free space for large crystal growth. KHCO 3 -Mg(OH) 2 solvent can be used to grow perovskite crystals. However, the carbonate solvent produces melt inclusions. Silicate sources with MgSiO 3 composition produce stishovite inclusions, which in turn cause splitting of perovskite crystals. The formation of these inclusions is avoided by using H 2 O as a solvent and 85MgSiO 3 -15Mg 2 SiO 4 as a silicate source. The H 2 O also allows homogeneous crystal growth, probably because of its low viscosity and high silicate solubility. High-quality single crystals larger than 1 mm were successfully synthesized through these technical developments.

Experiments were conducted to determine whether the presence of graphite is required to produce the Fe-Ti-P-enrichment, silica-depletion trend seen in ferrobasalts and ferrodiorites/jotunites. A nominally anhydrous Snake River Plain olivine tholeiite was crystallized at 9.3 kbar in Fe-Pt capsules; the composition of the Fe-Pt alloy was empirically chosen such that the charge neither lost nor gained iron. The results of these experiments and those of previous experiments conducted in graphite are strikingly similar: in both cases the residual liquids were depleted in silica and enriched in Fe, Ti, and P. We conclude that the presence of carbon is not essential for producing this distinctive trend.

Meridianiite, MgSO 4 ·11H 2 O, was recently discovered on the surface of a frozen pond in central British Columbia, Canada. Meridianiite is stable below 2 °C. Above 2 °C, it melts incongruently to a slurry of epsomite (MgSO 4 ·7H 2 O) and water. Magnesium sulfate minerals are thought to exist in the soils at Gusev crater and elsewhere on the Martian surface. These minerals can form by precipitation from a saturated solution or through evaporation of a brine solution at or below the surface. Meridianiite, instead of epsomite, is the expected magnesium sulfate phase in equilibrium with saturated brines below 2 °C on or below the Martian surface. It is expected to be the magnesium sulfate mineral in equilibrium with ice in the Martian polar ice caps. Meridianiite, if exposed to low humidity conditions in equatorial regions of Mars, would ultimately dehydrate to a fine dust of kieserite (MgSO 4 ·H 2 O) that could be dispersed by wind across the Martian surface. The name, meridianiite, was chosen to reflect the locality on Mars where the MER rover Opportunity observed crystal molds in sedimentary rock that are thought to be caused by minerals that have since dehydrated or dissolved.

Unit-cell lattice parameters have been measured to ~8 GPa in a diamond anvil cell for two single crystals of CaIrO 3 : one with the perovskite (Pbnm) and the other with the post-perovskite (Cmcm) structure. The CaIrO 3 post-perovskite structure is more compressible than the perovskite. A third-order Birch Murnaghan equation of state has been used to fit the measured P-V data with the following refined parameters: V 0 = 229.463(8) Å 3 , K 0 = 198(3) GPa, K’ = 1.2(8); and V 0 = 226.38(1) Å 3 , K 0 = 181(3) GPa, K’ = 2.3(8) for CaIrO 3 perovskite and post-perovskite, respectively. The compressibility of the unit-cell axes of the perovskite structure is highly anisotropic with β a >> β c >> β b . In contrast, the b axis is the most compressible in the post-perovskite structure, whereas the a and c axes have similar compressibilities (with c slightly less compressible than a) and are much stiffer. A comparison between the compressibility of CaIrO 3 perovskite and post-perovskite with the isostructural MgSiO 3 phases, reveals a similar general behavior, although in detail CaIrO 3 perovskite is more and the postperovskite less anisotropic than the corresponding MgSiO 3 compounds.

The hydrogen-carbonate ion [(HCO 3 ) - ] has been detected by Fourier transform infrared (FTIR) spectroscopy in the c-axis structural channel of Na-bearing type A-B carbonate apatite synthesized under conditions of high P (0.1-1 GPa), T (800-1350 °C), and p(CO 2 ), and accounts for up to one-third of the total complement of channel carbonate. The hydrogen-carbonate ion is only loosely bound in the apatite channel, and breaks down on aging at room temperature. Volatile decomposition products are lost from the carbonate apatite structure, with CO 2 more mobile than H 2 O. The mobility of small volatile molecules points to a possible role for the apatite channel in mediating acid-base reactions in restricted surficial environments and biological systems.

Radiation damage in a (initially crystalline) silicon wafer was generated by microbeam ion implantation with 600 keV Si + ions (fluence 5 × 10 14 ions/cm 2 ). To produce micro-areas with different degrees of damage, 14 implantations at different temperatures (between 23 and 225 °C) were done. The structural state of irradiated areas was characterized using Raman spectroscopy and electron back-scatter diffraction. All irradiated areas showed strong structural damage in surficial regions (estimated depth <1 μm), and at implant substrate temperatures of below 130 °C, the treatment caused complete amorphization. Back-scattered electron (BSE) image intensities correlate with the degree of irradiation damage; all irradiated areas were higher in BSE than the surrounding host. Because there were no variations in the chemical composition and, with that, no Z̅ contrast in our sample, this observation again supports the hypothesis that structural radiation damage may strongly affect BSE images of solids.

Ion microprobe analysis with a sub-micrometer diameter spot reveals a sharp, 2 μm gradient in oxygen isotope ratio proving that oxygen diffusion in zircon is slow even under prolonged high-grade metamorphism. The data are consistent with an oxygen diffusion coefficient of 10 -23.5±1 cm 2 /s. Furthermore, this gradient is found in a zircon that contains clear textural evidence of recrystallization in nearby regions. This finding shows that through careful textural and chemical analysis, primary information can be extracted from a zircon that has also undergone partial recrystallization. The oxygen isotope ratios found in zircon have been used to infer magmatic and pre-magmatic histories, including the presence of liquid water on the surface of earliest Earth. Recently, these interpretations have been questioned with the assertion that zircon may not retain its primary oxygen isotope signature through metamorphism. The slow diffusion confirmed by these results supports interpretations that assume preservation of magmatic compositions.