Volume 95, Issue 8-9

Electronic states of iron in Earth’s mantle minerals including ferropericlase, silicate perovskite, and post-perovskite have been previously investigated at high pressures and/or temperatures using various experimental techniques, including X-ray emission and Mössbauer spectroscopies. Although such methods have been used to infer changes in the electronic spin and valence states of iron in lower mantle minerals, they do not directly probe the 3d electronic states quantitatively. Here we use 1s2p resonant X-ray emission spectroscopy (RXES) at the Fe K pre-edge to directly probe and assess the 3d electronic states and the crystal-field splittings of Fe 2+ in the lower-mantle ferropericlase [(Mg 0.75 ,Fe 0.25 )O] at pressures up to 90 GPa. The pre-edge features from X-ray absorption spectroscopy in the partial fluorescence yield (PFY-XAS) and RXES results explicitly show three excited states for high-spin Fe 2+ (a lower-energy 4 T 1g state, a 4 T 2g state, and a higher-energy 4 T 1g state) and a single 2 E g state for low-spin Fe 2+ , attributed to the (t 2g ) 0 (e g ) 3 excited configuration. This latter feature begins to appear at 48 GPa and grows with pressure, while the peaks related to high-spin Fe 2+ vanish above 80 GPa. The observed pre-edge features are consistent with purely quadrupolar transitions resulting from the centrosymmetric character of the Fe 2+ site. The K pre-edge RXES spectra at the incident energy of 7112 eV, which are similar to the Fe L-edge spectra, are also used successfully to quantitatively obtain consistent results on the spin transition of Fe 2+ in ferropericlase under high pressures. Owing to the superior sensitivity of the RXES technique, the observed electronic states and their energy separations provide direct information on the local electronic structures and crystal-field splitting energies of the 3d electronic shells of Fe 2+ in ferropericlase at relevant pressures of the Earth’s lower mantle.

The metatorbernite [Cu(UO 2 ) 2 (PO 4 ) 2 ·8H 2 O] structure comprises autunite-type sheets of cornersharing uranyl square bipyramids and phosphate tetrahedra, with the interlayer region occupied by Cu 2+ ions and molecular water. Previous studies have shown that heating induces stepwise dehydration and reduction in basal spacing. Structures of the lower hydrates have not been determined previously because suitable single crystals of these phases have yet to be prepared. We have used synchrotron X-ray diffraction data collected during in situ, continuous heating of powdered metatorbernite to elucidate structures of its lower hydrates. Using Rietveld analysis, we have determined that autunite-type sheets remain intact through the first dehydration event above room temperature (onset 102 °C). We have discovered that the second dehydration event (onset 138 °C) triggers a major reconstruction to uranophane-type sheets, composed of chains of edge-sharing uranyl pentagonal bipyramids linked to one another by sharing edges and vertices with phosphate tetrahedra. This reconstruction enables the structure to overcome steric constraints on the minimum possible basal spacing, while maintaining Cu within the interlayer. Four distinct phases have been identified with increasing temperature: Cu(UO 2 ) 2 (PO 4 ) 2 ·8H 2 O, space group P4/n, a = 6.96519(23), c = 17.3102(8) Å; Cu(UO 2 ) 2 (PO 4 ) 2 ·6.1H 2 O, space group P4/n, a = 6.95510(29), c = 16.6604(9) Å; Cu(UO 2 ) 2 (PO 4 ) 2 ·3H 2 O, space group P2 1 , a = 14.4979(23), b = 7.0159(9), c = 6.6312(10) Å, β = 107.585(14)°; and a lower hydrate with monoclinic or triclinic symmetry, a ≈ 6.7, b ≈ 7, c ≈ 11 Å, β ≈ 100°. As shown here, in situ heating experiments and the Rietveld method provide fundamental insights into the crystal chemistry and structural behaviors of the important meta-autunite mineral group.

Fluorapatite grains from Apollo 15 Mare basalt 15058,128 were analyzed by Raman spectroscopy, Raman spectral imaging, time-of-flight secondary ion mass spectrometry (TOF-SIMS), field emission scanning electron microscopy (FE-SEM), and electron probe microanalysis (EPMA) in an attempt to detect structurally bound OH - in the fluorapatite. Although OH - could not be definitively detected by Raman spectroscopy because of REE-induced photoluminescence, hydroxyl was detected in the fluorapatite by TOF-SIMS. The TOF-SIMS technique is qualitative but capable of detecting the presence of hydroxyl even at trace levels. Electron microprobe data indicate that on average, F and Cl (F+Cl) fill the monovalent anion site in these fluorapatite grains within the uncertainties of the analyses (about 0.07 ± 0.01 atoms per formula unit). However, some individual spot analyses have F+Cl deficiencies greater than analytical uncertainties that could represent structural OH - . On the basis of EPMA data, the fluorapatite grain with the largest F + Cl deficiency constrains the upper limit of the OH- content to be no more than 4600 ± 2000 ppm by weight (the equivalent of ~2400 ± 1100 ppm water). The TOF-SIMS detection of OH - in fluorapatite from Apollo sample 15058,128 represents the first direct confirmation of structurally bound hydroxyl in a lunar magmatic mineral. This result provides justification for attributing at least some of the missing structural component in the monovalent anion site of other lunar fluorapatite grains to the presence of OH - . Moreover, this finding supports the presence of dissolved water in lunar magmas and the presence of at least some water within the lunar interior.

Radionuclide incorporation into the alteration products of corroded UO 2 in used nuclear fuel may control the release and mobility of key radionuclides, such as the very long-lived minor actinide, 237 Np (τ 1/2 = 2.1 Ma). Studtite, [UO 2 (O 2 )(H 2 O) 2 ](H 2 O) 2 , may form in the presence of peroxide produced by radiolysis of water in contact with the spent fuel. Experiments have indicated that the studtite structure can incorporate Np; however, due to the low concentrations in the solid, the incorporation mechanism could not be determined. In this study, density functional theory is used to calculate an optimized structure, determine the electronic density of states, and calculate the energetics of the incorporation of Np 6+ vs. Np 5+ + H + into the studtite structure. The definition of the source/sink phase (reference phase) for the cations involved in the incorporation process greatly affects the final incorporation energy. The incorporation energy of Np into studtite based on the 4 + oxide reference phases (e.g., source/sink = NpO 2 /UO 2 ) results in lower incorporation energies (-0.07 and 0.63 eV for Np 6+ and Np 5+ incorporation, respectively) than the incorporation energy calculated using higher-oxide reference phases (e.g., Np 2 O 5 /UO 3 ), where the incorporation energies for Np 6+ and Np 5+ into studtite are 0.42 and 1.12 eV, respectively. In addition, Np 6+ -incorporation into studtite is energetically more favorable than Np 5+ - incorporation as assessed from the lower incorporation energy. Estimates of the solid-solution behavior from a combination of quantum-mechanical calculations and Monte-Carlo simulations indicate that the Np 6+ - and U 6+ -studtite solid solution is completely miscible at room temperature with respect to a hypothetical Np6+-studtite structure. The Np-studtite structure was calculated to be stable with respect to the corresponding oxides, but its formation may be kinetically hindered. Knowledge of the electronic structure provides insight into Np-bonding in the studtite structure. The Np 5f orbitals are within the band gap of studtite, which results in the narrow band gap of Np-incorporated studtite (1.09 eV), as compared with the band gap of studtite alone (2.29 eV).

The V K-edge spectrum of a V-bearing grossular garnet (tsavorite) single crystal has been measured by high-energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS). Firstprinciples calculations based on the density functional theory (DFT) reproduce the experimental spectra well, including the angular dependence of the pre-edge. The latter arises from pure electric quadrupole transitions since vanadium is incorporated in a centrosymmetric site, which inhibits the electric dipole transitions. An interpretation of the spectral features is given using a monoelectronic description of the transitions involved in the X-ray absorption process. The assignment of experimental pre-edge peaks in terms of 1s-3d transitions makes it possible to determine the magnitude of the 3d-splitting, which is similar to the 10 Dq crystal-field value determined from optical absorption spectroscopy. DFT calculations also indicate a full structural relaxation around V 3+ substituting Al 3+ in the garnet structure. The angular dependence only causes weak variations of the pre-edge intensity, which supports the use of V-bearing grossular garnet as a reference compound for octahedral V 3+ .

Elbrusite-(Zr) Ca 3 (U 6+ Zr)(Fe 3+ 2 Fe 2+ )O 12 , a new uranian garnet (Ia3̅d, a ≈ 12.55 Å, V ≈ 1977 Å 3 , Z = 8), within the complex solid solution elbrusite-kimzeyite-toturite Ca 3 (U,Zr,Sn,Ti,Sb,Sc,Nb...) 2 (Fe,Al,Si,Ti) 3 O 12 was discovered in spurrite zones in skarn xenoliths of the Upper Chegem caldera. The empirical formula of holotype elbrusite-(Zr) with 25.14 wt% UO 3 is (Ca 3.040 Th 0.018 Y 0.001 ) Σ3.059 (U 6+ 0.658 Zr 1.040 Sn 0.230 Hf 0.009 Mg 0.004 ) Σ1.941 (Fe 3+ 1.575 Fe 2+ 0.559 Al 0.539 Ti 4 0.199 Si 0.099 Sn 0.025 V 5+ 0.004 ) Σ3 O 12 . Associated minerals are spurrite, rondorfite, wadalite, kimzeyite, perovskite, lakargiite, ellestadite-(OH), hillebrandite, afwillite, hydrocalumite, ettringite group minerals, and hydrogrossular. Elbrusite-(Zr) forms grains up to 10-15 μm in size with dominant {110} and minor {211} forms. It often occurs as zones and spots within Fe 3+ -dominant kimzeyite crystals up to 20-30 μm in size. The mineral is dark-brown to black with a brown streak. The density calculated on the basis of the empirical formula is 4.801 g/cm 3 The following broad bands are observed in the Raman spectra of elbrusite-(Zr): 730, 478, 273, 222, and 135 cm -1 . Elbrusite-(Zr) is radioactive and nearly completely metamict. The calculated cumulative dose (α-decay events/mg) of the studied garnets varies from 2.50 × 10 14 [is equivalent to 0.04 displacement per atom (dpa)] for uranian kimzeyite (3.36 wt% UO 3 ), up to 2.05 × 10 15 (0.40 dpa) for elbrusite-(Zr) with 27.09 wt% UO 3 .

Petrologic, chemical, and polytype data are presented for dioctahedral potassic micas from Kfeldspar- bearing metamorphic and igneous rocks of acidic composition unaffected by high-pressure (HP) conditions. The paper aims to demonstrate that: (1) under non-HP conditions, in both metamorphic and igneous plutonic environments, a given bulk-rock compositional constraint imposes a more or less marked phengitic composition to dioctahedral potassic mica; and (2) this muscovite crystallizes as 2M 1 , notwithstanding its phengitic composition. The samples (157 in number) are from widespread provenances. We conclude that the growth of 3T polytype of muscovite is not a function of mica composition. This is consistent with the recent crystallographic knowledge on polytypism, cation ordering, elastic properties, and structural deformational mechanisms of muscovite, which address the stabilization of 3T with pressure.

Radiation damage of natural and synthetic zircon grains is evaluated by Raman spectroscopy to understand annealing and stability of fission tracks. Analyses focus on a suite of 338 Paleozoic detrital zircon grains from metamorphosed strata in the Hellenic forearc that were variably annealed by a Miocene thermal event, as well as a suite of 97 synthetic zircon grains. The Raman wavenumber shift of ν 3 [SiO 4 ] reveals that radiation damage and damage distribution in this suite mainly depends on uranium concentration. In zircon with similar uranium concentration, the Raman wavenumber shift allows for the determination of radiation damage in different crystals, which is a function of effective accumulation time. Nine detrital zircons grains with moderate radiation damage were stepwise annealed at 1000 and 1400 °C, which resulted in progressive removal of radiation damage revealed in an increase of ν 3 [SiO 4 ] peak positions. For a partly reset sample that was brought to temperatures of ~350 °C in a geologic setting (Hellenic forearc), we use the Raman measurements and uranium determination to estimate a Zircon Damage Discrimination Factor (Z RDD ), which is our attempt to estimate only radiation damage in single grains by accounting for affects of the uranium atom in the Raman wavenumber. This discrimination allows for a separation of zircon fission track (ZFT) ages of single ages based on grains that have a low track retention (high damage, fully reset grain), thus refining the age determination of cooling in a rock that shows variable resetting.

Poorly crystalline solids play an important role in many low-temperature geochemical processes, such as trace element speciation and biomineralization. Yet, the structures of many such naturally occurring phases are poorly understood. X-ray absorption spectroscopy is a powerful tool that permits chemically and spatially resolved investigations of poorly crystalline materials. In this study, we compare structural and electronic information derived from different regions of chromium K-edge X-ray absorption spectra for a series of poorly ordered iron(III)-chromium(III)-oxyhydroxides. These phases regularly form after the reduction of Cr(VI) by Fe(II) and often dictate the long-term fate of Cr in the environment. The distinct parts of the X-ray absorption spectrum, namely the pre-edge region, the near edge (XANES) region, and the extended (EXAFS) region, provide complementary information about the local chemical environment of Cr. Analysis of the XANES and EXAFS spectra showed that the structure around Cr in the Cr-poor sample is primarily composed of edge-sharing octahedra, whereas the octahedra in the Cr-rich samples are connected by edge-sharing and cornersharing linkages. The analysis of non-local transitions in the pre-edge spectra indicated the absence of Cr clustering at low Cr substitution. This study demonstrates the advantage of complementary pre-edge, XANES, and EXAFS analysis to deduce information on the medium-range environment around Cr in poorly ordered solids.

Oceanic-type high-pressure eclogite from the Huwan mélange in the western part of the Dabie orogen, north of the classic ultrahigh-pressure terrane, has been investigated with combined Lu-Hf and Sm-Nd geochronology. The eclogites are thought to have formed during the subduction of oceanic crust prior to the subduction of the Yangtze craton beneath the North China block. Garnet Lu-Hf and Sm-Nd garnet-whole rock dates yield similar ages of 257.4 ± 1.4 and 252.5 ± 2.7 Ma, the youngest ages reported thus far from this mélange. Despite the partially preserved prograde major- and traceelement zoning in garnets, the Lu-Hf and Sm-Nd ages mostly reflect the high-pressure eclogite-facies metamorphism instead of the early phase of garnet growth. The data define a new high-pressure age population for the Dabie orogen, which provides a more detailed insight into the subduction history of the Yangtze craton before continental collision. The new Lu-Hf and Sm-Nd dates for these oceanictype eclogites, combined with existing geochronological information, range from 315 to 253 Ma. This broad interval suggests that the overall subduction of oceanic crust occurred over a period of ~60 Ma and that different slices with distinct pressure-temperature histories underwent HP metamorphism at distinct times. A model of a continuous evolution from oceanic to continental subduction is favored, and the onset of the deeply continental subduction occurred probably not before ca. 257 Ma.

Formation of hydroxylapatite through the precipitation and evolution of calcium phosphate precursor phases under varying conditions of temperature (25-90 °C), pH (6.5-9.0), and calcium to phosphorus ratio (1.0, 1.33, 1.5, and 1.67) comparable to those found in many sediments and soils were studied. The products of low-temperature precipitation were analyzed by ex situ X-ray diffraction and SEM, as well as time-resolved in situ synchrotron X-ray diffraction. Rietveld refinement was used for quantitative evaluation of relative abundances during phase evolution. The results of ex situ investigations conducted at ambient temperature and near-neutral pH indicate formation of amorphous calcium phosphate, which over the course of experiments transforms to brushite and ultimately hydroxylapatite. The results of in situ X-ray diffraction experiments suggest a more complex pathway of phase development under the same conditions. Some of the initially formed amorphous calcium phosphate and/or crystalline brushite transformed to octacalcium phosphate. In the later stage of the reactions, octacalcium phosphate transforms quite rapidly to hydroxylapatite. This is accompanied or followed by the transformation of the remaining brushite to monetite. Hydroxylapatite and monetite coexist in the sample throughout the remainder of the experiments. In contrast to the near-neutral pH experiments, the results from ex situ and in situ diffraction investigations performed at higher pH yield similar results. The precipitate formed in the initial stages in both types of experiments was identified as amorphous calcium phosphate, which over the course of the reaction quite rapidly transformed to hydroxylapatite without any apparent intermediate phases. This is the first application of time-resolved in situ synchrotron X-ray diffraction to precipitation reactions in the Ca(OH) 2 -H 3 PO 4 -H 2 O system. The results indicate that precursors are likely to occur during the natural or induced (e.g., with application of Ca+PO 4 amendments) formation of hydroxylapatite in many sedimentary environments.

Fe 3+ and Mn 3+ distributions on octahedral M1, M2, and M3 sites in synthetic epidote/piemontite from Ca 2 Al 2 Fe 3+ q Mn 3+ 1-q Si 3 O 12.5 starting material and their effects on the crystal structure were investigated using X-ray Rietveld and 57 Fe Mössbauer methods. Epidote and piemontite were crystallized as almost single phases from q = 1.0, 0.75, 0.5, and 0.25 starting materials at Pfluid of 200-400 MPa and a temperature of 500 °C, using standard cold-seal pressure vessels. The Mn 2 O 3 -MnO 2 buffer was used to produce f O₂ adequate to maintain Fe 3+ and Mn 3+ . The Rietveld refinements converged to goodness-of-fit ranges from 1.21 to 1.60. At this temperature, site preferences of Σ(Fe 3+ +Mn 3+ ) for octahedral sites are M3>M1(>>M2). K D values of Σ(Fe 3+ +Mn 3+ ), where K D = [(Fe 3+ +Mn 3+ )/Al] M1 /[(Fe 3+ +Mn 3+ )/Al] M3 , (0.05-0.13) are similar to those of individual Mn 3+ and Fe 3+ vs. Al 3+ , respectively. However, the K D values of Fe 3+ and Mn 3+ for M1 and M3, where K D = (Fe 3+ /Mn 3+ ) M1 /(Fe 3+ /Mn 3+ ) M3 , vary with Fe 3+ Total:Mn 3+ Total ratios. In epidote with Fe 3+ content larger than 0.4 atoms per formula unit (apfu) and Mn 3+ < 0.6 apfu, Fe 3+ has a stronger preference for M1 than Mn 3+ . In piemontite with 0.12 Fe 3+ and 0.73-0.78 Mn 3+ apfu, the preference of Mn 3+ for M1 is greater than that of Fe 3+ . The site occupancies of individual Mn 3+ and Fe 3+ are governed by the individual K D values and the Mn 3+ and Fe 3+ concentrations in corresponding epidote and piemontite. Variations of the unit-cell parameters indicate the combined result of linear variation due to Al ↔ Fe 3+ substitution and nonlinear variation due to Al ↔ Mn 3+ substitution.

This paper reports the results of an in situ high-pressure synchrotron X-ray powder diffraction investigation on the natural zeolite boggsite [(K 0.06 Na 0.36 Sr 0.01 Ca 7.00 Mg 1.20 )(Al 17.52 Si 78.62 Fe 0.05 O 192 )·82.3 H 2 O]. The study was performed using both a (16:3:1) methanol:ethanol:water mixture (m.e.w.) as a nominally “penetrating” hydrostatic P-transmitting medium and silicon oil (s.o.) as a “non-penetrating” medium. The studied pressure ranges are: P amb -7.6 and P amb -5.9 GPa in m.e.w and s.o., respectively. No complete X-ray amorphization is observed up to the highest investigated pressures, and the original unit-cell parameters are almost completely recovered upon decompression in both media. The reductions of a, b, c, and V, within the pressure-ranges investigated, are 5.3, 4.2, 4.0, and 13.0% in s.o. and 4.1, 4.1, 3.8, and 11.5% in m.e.w. The Rietveld structural refinements of the powder patterns of the experiments in m.e.w. converged successfully up to 3.6 GPa and demonstrated the penetration of 13 additional water molecules between 0.3 and 2.9 GPa. This over-hydration occurs without any unit-cell volume expansion and can be explained by the fact that no new extraframework sites arise during compression and that water penetration is the only factor to increase the occupancy of already existing sites. Boggsite compressibility is higher in s.o. than in m.e.w. In particular, compressibility in m.e.w. is lower below 3 GPa, whereas above this pressure, the P-V trend becomes similar in the two media. This can be ascribed to the fact that, during water molecule penetration (0.3 < P < 3 GPa), the effect of the P-transmitting medium is directed to compress the system as well as to penetrate the channels.

The powder-transmission infrared spectra of OH-stretching modes in well-ordered samples of kaolinite and dickite are recorded from 270 to 10 K. Effective medium modeling of the kaolinite spectrum confirms the coupled motion of non-equivalent OH groups in the inter-layer OH-stretching modes. A full assignment of OH-stretching bands in dickite is proposed. In particular, the band observed at 3685 cm-1 in room-temperature spectra is attributed to a kaolinite-like defect, whereas that at 3706 cm -1 is related to OH3 groups of the dickite structure. The changes in phonon frequency and line shape are analyzed as a function of temperature. The results evidence the quasi-harmonic nature of the OH-stretching modes in kaolinite-group minerals. Coupling of OH-stretching modes to each other can be related to the macroscopic electrostatic properties of the composite medium, made of mineral particles and KBr matrix, and not to microscopic anharmonic mechanisms. The low saturation temperatures of vibrational frequencies and linewidths indicate that the OH-stretching modes probe the average thermal bath of the crystal, without coupling to a specific decay channel

This research investigated the phase transition between low- and high-temperature orthopyroxenes with composition (Ca 0.06 Mg 1.94 )Si 2 O 6 using differential scanning calorimetry experiments and in situ high-temperature X-ray diffraction. The transition enthalpy, temperature, volume change, and slope were estimated to be 6.2 kJ/mol, 1170 °C, 10.25 Å 3 /unit cell, and 0.0056 GPa/°C, respectively. The phase boundary between low- and high-temperature orthopyroxene was defined as P (GPa) = 0.0056T (°C) - 6.55. This relationship shows that the invariant point for four-phase equilibria (protoenstatite + high-temperature orthopyroxene + pigeonite + diopside) is approximately 1240-1280 °C and 0.1-0.2 GPa, rather than the equivalent system involving low-temperature orthopyroxene as described in previous studies. We developed phase diagrams for Mg 2 Si 2 O 6 and the Mg 2 Si 2 O 6 -CaMgSi 2 O 6 system taking into account the results of previous synthetic experiments and the phase boundary that we determined between low- and high-temperature orthopyroxene. The developed phase diagrams for Mg 2 Si 2 O 6 showed that high-temperature orthoenstatite is more stable than protoenstatite at pressure above ~0.8 GPa, and that the boundary between high-temperature orthoenstatite and protoenstatite has a gentle negative slope. As pressure is increased from 1 atm to about 0.2 GPa, the lower temperature limit of stability of high-temperature orthopyroxene decreases from ~1370 to ~1200 °C. Above 0.9 GPa, the stability field of protoenstatite disappears and high-temperature Ca-free orthopyroxene is stable. On the basis of these results, it is suggested that further high-resolution analyses of the thermodynamics of the enstatite-diopside system at high temperatures and high pressures are required.

A new polymorph of topaz-OH (denoted as topaz-OH II) was recently discovered at higher P-T conditions than has been known thus far (denoted as topaz-OH I). High-resolution 1 H, 29 Si, and 27 Al nuclear magnetic resonance (NMR) and micro-Raman spectroscopy are applied to shed light on the crystal chemistry of both polymorphs. Topaz-OH I, synthesized at 7 GPa and 640 °C, is stoichiometric (Si/Al = 0.5) with a largely ordered local structure. Higher P-T topaz-OH I synthesized at conditions close to the polymorphic phase transition boundary, on the other hand, shows lower Si/Al ratios (0.44-0.45) and greater local structural disorder [including a small fraction (~3%) of octahedral Si with a unique 29 Si chemical shift near -133 ppm]. The latter may be accounted for by the development of defects (Si/Al in normally vacant octahedral sites and vacancies in the tetrahedral sites) at higher P-T conditions. Topaz-OH II synthesized at 13.5~14 GPa and 1300~1400 °C similarly exhibits low Si/Al ratios (0.41-0.46). The NMR and Raman spectra for these topaz-OH II are, in general, broader and revealed a substantial fraction (33-37%) of octahedral Si with a range of 29 Si chemical shifts (-130 to -190 ppm), a small fraction (2-3%) of tetrahedral Al, and a range of (and overall shorter) hydrogen-bonding distances than topaz-OH I. Therefore, the phase transition from topaz-OH I to II is characterized by both a significant increase in the occupied octahedral/tetrahedral site ratio as well as disordering of cation distribution, which is unique from the viewpoint of crystal chemistry.

The crystal structure and crystal chemistry of chromian pumpellyite from basic schist in the Osayama ultramafic body, Okayama, Japan, were investigated using electron probe microanalysis (EPMA), Fourier transform infrared spectroscopy (FTIR), and single-crystal X-ray diffraction to determine the distribution of chromium between two independent octahedral sites and structural changes caused by ionic substitutions in pumpellyite, VII W 8 VI X 4 VI Y 8 IV Z 12 O 56-n (OH)n (Z = 1). Five chromian pumpellyite crystals (ocp1211, ocp0604, ocp1028, ocp1013, and ocp1016) with 0.52, 1.65, 1.26, 1.94, and 1.43 Cr atoms per formula unit (apfu) (EPMA data), respectively, were picked from a hand specimen for X-ray diffraction analysis. The crystal structures (space group C2/m) of ocp1211 [a = 19.1129(6), b = 5.8963(5), c = 8.818(1) Å, β = 97.449(2)°], ocp0604 [a = 19.0935(4), b = 5.900(1), c = 8.810(2) Å, β = 97.540(7)°], ocp1028 [a = 19.105(2), b = 5.9021(6), c = 8.8143(7) Å, β = 97.513(3)°], ocp1013 [a = 19.1558(6), b = 5.9125(9), c = 8.844(1) Å, β = 97.448(4)°], and ocp1016 [a = 19.174(3), b = 5.9194(8), c = 8.830(1) Å, β = 97.497(4)°] were refined using 1058, 829, 1070, 1105, and 1095 unique reflections, and calculations converged at R factors of 4.08, 5.02, 6.32, 6.92, and 7.88%, respectively. The resulting site populations at the X and Y sites are (Mg 1.88 Al 1.51 Fe 2+ 0.38 Cr 0.16 Mn 2+ 0.05 Ni 0.02 ) X (Al 7.90 Ti 0.07 V 0.03 ) Y for ocp1211, (Mg 1.81 Al 1.53 Cr 0.42 Fe 2+ 0.18 Mn 2+ 0.04 Ni 0.01 ) X (Al 7.34 Cr 0.65 V 0.01 ) Y for ocp0604, (Al 1.62 Mg 1.60 Cr 0.61 Fe 2+ 0.13 Mn 2+ 0.03 Ni 0.01 ) X (Al 7.36 Cr 0.61 V 0.03 ) Y for ocp1028, (Mg 1.79 Al 1.33 Cr 0.47 Fe 2+ 0.33 Mn 2+ 0.08 ) X (Al 6.66 Cr 1.31 V 0.03 ) Y for ocp1013, and (Mg 1.94 Al 1.23 Cr 0.38 Fe 2+ 0.37 Mn 2+ 0.08 ) X (Al 6.72 Cr 1.25 V 0.03 ) Y for ocp1016. Cr 3+ ions in ocp1211 are distributed only in the X site. The distribution coefficient of Cr and Al between the X and Y sites [(Cr/Al) X /(Cr/Al) Y ] is 1.66, 1.79, 3.09, and 4.54 for ocp1016, ocp1013, ocp0604, and ocp1028, respectively, indicating a stronger preference of Cr for the X site than the Y site. The a and b axes increase with increasing Cr content, whereas the c axis is almost constant. The mean Y-O distances increase linearly with increased Cr 3+ content in the Y site. However, the mean X-O distances do not depend on the substitution of Cr 3+ for Al 3+ at the X site. The bond valence sums and the difference-Fourier synthesis indicate that hydroxyl groups are located at the O5, O7, O10, and O11 positions. FTIR spectrum shows main absorption bands at ca. 2911, 3220, 3397, and 3512 cm -1 of OH-stretching vibrations, indicating the presence of OH⋅⋅⋅O hydrogen bonds.

A new Sn-rich garnet, toturite Ca 3 Sn 2 Fe 2 SiO 12 , occurs as an accessory mineral in high-temperature altered carbonate-silicate xenoliths in ignimbrite of the Upper Chegem structure in the Northern Caucasus, Kabardino-Balkaria, Russia. The empirical formula of toturite from the holotype sample is (Ca 2.989 Fe 2+ 0.011) Σ3 (Sn 4+ 1.463 Sb 5+ 0.325 Ti 4+ 0.193 Zr 0.013 Mg 0.003 Nb 5+ 0.002 Cr 0.001 ) Σ2 (Fe 3+ 1.633 Al 0.609 Si 0.552 Ti 4+ 0.166 Fe 2+ 0.039 V 5+ 0.001 ) Σ3 O 12 . The mineral forms thin regular growth zones and irregular spots in the Fe 3+ -dominant analog of kimzeyite. Toturite is cubic, Ia3̅d, a ≈ 12.55 Å, as is confirmed by electron backscatter diffraction (EBSD) data. The strongest lines of the calculated powder diffraction pattern are [d, Å (hkl) I]: 2.562 (422) 100, 1.677 (642) 91, 3.138 (400) 74, 4.437 (220) 67, 1.146 (10.4.2) 31, 1.046 (884) 25, 1.984 (620) 23. Raman spectra of toturite are analogous to those of kimzeyite and shows the following diagnostic bands (cm -1 ): 244, 301, 494, 497, 575, 734. The association of toturite with larnite, rondorfite, wadalite, magnesioferrite, lakargiite, and cuspidine indicates a high temperature (>800 °C) of formation. The mineral name is given after the Totur River situated in Eltyubyu village, also Totur is the name of a Balkarian god.

Schwertmannite is a poorly crystalline mineral that forms ochre rusts and precipitates in acid mine environments. Despite its ubiquity and its role as scavenger of important contaminants such as arsenic or selenium, its structure has not been yet determined. Here, a structure for schwertmannite is presented based on pair distribution function (PDF) data, X-ray diffraction (XRD) analyses, and density functional theory (DFT) calculations. We propose a structure formed by a deformed frame of iron octahedra similar to that of akaganeite. Simulations of X-ray diffraction patterns unveil the presence of long-range order associated with the position of the sulfate molecules, providing a useful way to discern two types of sulfate complexes in the structure. The simulations suggest that two sulfate molecules per unit cell are present in the structure forming one outer sphere and one inner sphere complex inside the channels formed by iron octahedra. Knowledge of the positions of the sulfates in the structure will help to better understand exchange processes with oxyanions of trace contaminants, such as arsenate, chromate, or selenate, that strongly influence their biogeochemical cycling in mining ecosystems.

The crystal chemistry of some Cr-spinels from the lherzolite body of the Ronda peridotite in southern Spain has been investigated. Cell edge spans between 8.1692(2) and 8.2367(1) Å, while the oxygen positional parameter u ranges between 0.26306(7) and 0.26351(7). By using the Princivalle thermometer (1999), an intracrystalline closure temperature between 640 and 840 °C has been calculated. The higher temperatures are very close to the intercrystalline temperatures based on the olivine-spinel thermometer calculated by Woodland et al. (2006) for the Ronda orogenic lherzolites suggesting that the intracrystalline closure occurred soon after the intercrystalline closure. By comparison with Cr-spinels from lherzolite mantle xenoliths, it should be noted that: (1) the oxygen positional parameter can be linearly related to the intracrystalline temperature for both mantle peridotite and mantle xenolith Cr-spinels; (2) the intracrystalline closure temperature is reached faster and is higher in Cr-spinels in mantle xenoliths; and (3) Cr content is linearly related to u in mantle peridotite, but not in mantle xenoliths, suggesting the u value in Cr-spinels from mantle peridotite is driven solely by the chemistry of the spinels.

Ottoite, Pb 2 TeO 5 , is a new tellurate from Otto Mountain near Baker, California. Most of the mining on Otto Mountain occurred between 1940 and 1970 and is attributed to Otto Fuetterer, for whom the mountain is now named. The new mineral occurs on fracture surfaces and in small vugs in brecciated quartz veins, which intersect granitic rocks. Ottoite is directly associated with acanthite, bromine-rich chlorargyrite, gold, iodargyrite, khinite, wulfenite, and four other new tellurates: housleyite, markcooperite, thorneite, and timroseite. Various other secondary minerals occur in the veins, including two other new secondary tellurium minerals, paratimroseite and telluroperite. Ottoite and most other secondary minerals of the quartz veins are interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of the veins. A later generation of quartz mineralization then recemented the breccias, effectively isolating and protecting the secondary mineralization from further alteration. Ottoite is monoclinic, space group I2/a, with the unit cell: a = 7.5353(6), b = 5.7142(5), c = 10.8981(12) Å, β = 91.330(6)°, V = 469.13(8) Å 3 , and Z = 4. The mineral occurs as complex spear-shaped crystals in subparallel to divergent intergrowths. It is yellow and transparent to translucent, with a pale yellow streak and adamantine luster. Mohs hardness is estimated at 3. The mineral is brittle, with an irregular fracture and two cleavages in the [100] zone at ~90°-possibly on {010} and {001}. The calculated density is 8.721 g/cm 3 . Ottoite is biaxial (-), with a large 2V, but indices of refraction are too high to be measured. The optic orientation could only partially be determined: Y ≈ a. No pleochroism was observed. Electron microprobe analyses provided the following averages: PbO 68.88 and TeO 3 28.03, total 96.95 wt%; the empirical formula (based on O = 5) is Pb 1.96 Te 6+ 1.01 O 5 . The strongest powder X-ray diffraction lines are [d obs in Å (hkl) I]: 3.131 (2̅02) 64, 3.055 (013) 90, 3.015 (211) 100, 2.112 (2̅22) 29, 1.810 (006, 2̅15) 21, 1.773 (4̅11, 402) 43, 1.686 (033, 231) 20. The crystal structure (R 1 = 0.020) consists of straight chains of trans-corner-sharing Te 6+ O 6 octahedra parallel to a, which are joined by bonds to Pb atoms. The Pb atom exhibit markedly lopsided 11-coordination, typical of Pb 2+ with stereoactive 6s 2 lone-pair electrons. The powder X-ray diffraction pattern of ottoite is very similar to that reported for girdite. Examination of girdite type material suggests that its description was based upon data obtained from at least two and possibly three different phases, one of which may correspond to ottoite.

Housleyite, Pb 6 CuTe 4 O 18 (OH) 2 , is a new tellurate from Otto Mountain near Baker, California, named in honor of Robert M. Housley. The new mineral occurs on fracture surfaces and in small vugs in brecciated quartz veins. Housleyite is directly associated with acanthite, cerussite, gold, iodargyrite, khinite-4O, wulfenite, and three other new tellurates: markcooperite, ottoite, and thorneite. A variety of other secondary minerals occur in the veins, including three other new secondary tellurium minerals, paratimroseite, telluroperite, and timroseite. Housleyite is monoclinic, space group P2 1 /n, a = 7.8552(5), b = 10.4836(7), c = 11.0426(8) Å, β = 95.547(2)°, and Z = 2. Crystals are prismatic to bladed with elongation parallel to b and typically occur in bow tie-like aggregates, drusy balls, and irregular sprays. It is pale to medium greenish blue and transparent, with pale blue streak and adamantine luster. Mohs hardness is estimated at 3. The mineral is brittle, with an irregular fracture. Cleavage was not observed, but is likely on {101}. The calculated density is 7.845(1) g/cm 3 . Housleyite is biaxial (+), with 2V = 50° to 60° and strong inclined dispersion, r > v, but indices of refraction are too high to be measured. The optic orientation is Y = b, Z ^ c ≈ 40° in obtuse β and pleochroism is Y (medium green-blue) > Z (light green-blue) > X. Energy dispersive spectroscopy provided PbO 62.53, CuO 3.77, TeO 3 32.85, H 2 O 0.84 (structure), total 99.99 wt%.; the empirical formula (based on O = 20) is Pb 5.99 Cu 1.01 Te 4.00 O 18 (OH) 2 . The strongest powder X-ray diffraction lines are [dobs in Å (hkl) I]: 3.336 (2̅02, 031, 122) 69, 3.292 (1̅13) 50, 3.195 (130, 103) 100, 3.068 (2̅21, 202) 47, 3.007 (023) 49, 2.942 (032, 212) 80, 2.723 (123, 2̅13, 132) 29, 2.580 (230, 3̅01, 2̅31) 38. The crystal structure (R 1 = 0.028) consists of corner-sharing chains of TeO 6 octahedra along [101] linked into slabs parallel to {101̅} by sharing edges and corners with strongly Jahn-Teller (4+2) distorted and severely skewed CuO 6 octahedra. Lead (Pb) atoms in lopsided nine- and elevenfold coordinations form additional links within and between the octahedral sheets.

The application of the Hf isotope composition of zircon as a geochemical tracer requires the preservation of Lu-Hf systematics within individual grains. We performed hydrothermal experiments on a self-irradiation-damaged zircon to test whether hydrothermal alteration would affect its Hf isotopic composition. Severely radiation-damaged zircon from Sri Lanka was reacted in either Teflon reactors or gold capsules at 200 °C (1080 h, autogeneous pressure), 400 °C (120 h, 1 kbar), and 600 °C (72 h, 1 kbar) in a 1 M HCl-0.2 M HF solution that was spiked with 300 ppm non-natural Hf (98.2% 180 Hf) and 970 ppm Yb. Laser ablation inductively coupled plasma mass spectrometry measurements of the Hf- and U-Pb isotope compositions of the altered domains revealed that the U-Pb system of such domains was severely disturbed, resulting in a discordia pointing toward the origin of the concordia diagram, but that the Hf isotope composition was unaffected. In addition, Yb enrichment was observed in the reacted zircon domains, predominantly near the zircon-solution interface. The Yb has apparently diffused into the altered domains. The new data are fully consistent with a diffusion-controlled aqueous alteration process occurring within radiation-damaged zircon.

A new high-pressure form of topaz-OH (denoted here topaz-OH II) was obtained at 14 GPa and 1400 °C. The X-ray diffraction pattern of this phase can be indexed by an orthorhombic cell with a = 4.72318(5), b = 8.91480(9), and c = 2.77276(3) Å. The lengths of a and b are similar, but c is approximately a third of that for a previously reported topaz-OH (denoted topaz-OH I). The structural formula of topaz-OH II can be written as (Al 0.68 Si 0.32 )(O 0.66 (OH) 0.34 ) 2 , suggesting significant cation disorder in the structure. The crystal structure of topaz-OH II is solved using powder synchrotron X-ray diffraction data, and refined with constraints provided by a separate multi-nuclear NMR study. The structure has similarities with topaz-OH I and diaspore (α-AlOOH) structures, having partially occupied double edge-shared octahedral chains, and 2 × 1 tunnels with partially occupied tetrahedral and octahedral sites.

We report the application of high-resolution in situ 238 U- 230 Th disequilibrium dating to pyrochlore [(Ca,Na,REE,Th,U) 2 (Nb,Ti,Ta,Zr) 2 O 6 (OH,F)]. Compositionally zoned pyrochlore is an accessory phase in intrusive carbonatitic syenites, which were ejected as cognate clasts during the eruption of the phonolitic Laacher See volcano, East Eifel, Germany, 12.9 ka ago. Separated individual pyrochlore crystals were analyzed for U-Th isotopes and elemental abundances at high spatial resolution (~25 μm) using secondary ion mass spectrometry (SIMS) with an internal precision for the 238 U- 230 Th isochron of ~700 a (2σ). U and Th were also analyzed by electron microprobe in SIMS spots. Instrumental mass fractionation for Th/U was corrected using an EMP vs. SIMS calibration curve, and the resulting pyrochlore isochron age of 26.1 ± 1.4 ka (including external calibration uncertainty) is concordant with the 23 +7/-6 ka U-Th zircon ages for the same sample. By contrast, AM206 pyrochlore from a Cretaceous alkali granite shows significant disequilibrium with ( 230 Th)/( 238 U) = 0.90 ± 0.04. The tightly defined isochron implies that U-Th in Laacher See pyrochlore remained a closed decay system during protracted residence in the magma chamber carapace, and was unaffected by hydrothermal alteration or post-eruptive weathering over time scales of tens of thousands of years. By contrast, disequilibrium in AM206 pyrochlore indicates U-Th mobilization during protracted near-surface residence.