Hydrogen diffusion in Dora Maira pyrope

Kinetics of hydrogen extraction were investigated by FTIR spectroscopy on a Dora Maira pyrope single crystal. Annealing experiments were performed at ambient pressure, between 1073 and 1323 K, and under two different redox conditions (pO₂=0.21 atm and pO₂ 10^–16 atm). During hydrogen extraction the two principal OH absorption bands behave independently. The OHa triplet, centred on 3651 cm^–1, decreases at least five times faster than the OHb band at 3602 cm^–1. This suggests the presence of two distinct H defects, each with its own kinetics, which are slightly dependent on oxygen partial pressure:Both kinetics are slower than previous data (Wang et al. 1996), but activation energies are similar. At the same time as the OHa bands decrease, an exchange of hydrogen from OHa to OHb occurs. The extent of this transfer can be modelled by assuming it is directly proportional to the fraction of OHa band which has been removed, independent of temperature. This suggests that OHb defects could be produced by partial dehydrogenation of OHa defects. Activation energies and values of diffusion coefficients are very close to those found by Kohlstedt and Mackwell (1998) for the diffusion of metal vacancies in olivine. Thus it is very likely that cation vacancies control the kinetics of dehydrogenation reactions in pyrope.     

Local relaxation around [6]Cr 3+ in synthetic pyrope–knorringite garnets, [8]Mg 3 [6](Al 1-X Cr X 3+) 2 [4]Si 3O 12, from electronic absorption spectra

Pyrope-knorringite garnets, Mg₃(Al_1-X Cr³⁺_X)₂Si₃O₁₂ with X=0.25, 0.50, and 1.00, were synthesized between 9 and 16 GPa and 1300 and 1600 °C, using multianvil high-pressure techniques. The garnets with X=0.25 and 0.50 are fine-grained, pink and violet in color. The end-member knorringites with X=1.00 are black when compact and gray when coarse-grained. The fine powder is greenish gray in natural light and pale pink under a tungsten lamp. Powder remission spectra in the wavenumber range 30 000–10 000 cm^–1 on finely powdered crystals were measured by two different methods: (I.) by the use of a small integrating sphere for small samples or (II.) microscope-spectrometric measurement using diffusely reflected radiation from a 45° illuminated microsample. Both methods yielded similar diffuse reflectance spectra. The following crystal-field parameters of ^[6]Cr³⁺ were determined for garnets with X=0.25, 0.50, 1.00: 10 Dq=17 856, 17 596, 17 286 cm^–1; and B=654, 677, 706 cm^–1; nephelauxetic ratio =(B_field/B_free)= 0.71, 0.74, 0.77. The -values indicate decreasing covalency of the Cr–O bond with increasing Cr content. The 10 Dq value for together with the mean Cr–O distance in end-member knorringite, 1.96 Å (Novak and Gibbs 1971), were used to calculate from the spectral data, local mean Cr–O distances (Langer 2001a) as a function of composition. The results indicate relatively strong local site relaxation with a value of =0.77.     

Fe<Superscript>3+</Superscript> reduction during biotite melting in graphitic metapelites: another origin of CO<Subscript>2</Subscript> in granulites

The Fe³⁺/Fe_tot of all Fe-bearing minerals has been analysed by Mössbauer spectroscopy in a suite of biotite-rich to biotite-free graphitic metapelite xenoliths, proxies of an amphibolite-granulite transition through progressive biotite melting. Biotite contains 9 to 16% Fe³⁺/Fe_tot, whereas garnet, cordierite and ilmenite are virtually Fe³⁺ -free (0–1% Fe³⁺/Fe_tot) in all samples, regardless of biotite presence. Under relatively reducing conditions (graphite-bearing assemblages), biotite is the only carrier of Fe³⁺ during high-temperature metamorphism; therefore, its disappearance by melting represents an important event of iron reduction during granulite formation, because haplogranitic melts usually incorporate small amounts of ferric iron. Iron reduction is accompanied by the oxidation of carbon and the production of CO₂, according to the redox reaction:

Thermodynamic properties,low-temperature heat-capacity anomalies,and single-crystal X-ray refinement of hydronium jarosite, (H<Subscript>3</Subscript>O)Fe<Subscript>3</Subscript>(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)<Subscript>6</Subscript>

Crystals of hydronium jarosite were synthesized by hydrothermal treatment of Fe(III)–SO₄ solutions. Single-crystal XRD refinement with R₁=0.0232 for the unique observed reflections (|F_o| > 4_F) and wR₂=0.0451 for all data gave a=7.3559(8) Å, c=17.019(3) Å, V^o=160.11(4) cm³, and fractional positions for all atoms except the H in the H₃O groups. The chemical composition of this sample is described by the formula (H₃O)_0.91Fe_2.91(SO₄)₂[(OH)_5.64(H₂O)_0.18]. The enthalpy of formation (H^o_f) is –3694.5 ± 4.6 kJ mol^–1, calculated from acid (5.0 N HCl) solution calorimetry data for hydronium jarosite, -FeOOH, MgO, H₂O, and -MgSO₄. The entropy at standard temperature and pressure (S^o) is 438.9±0.7 J mol^–1 K^–1, calculated from adiabatic and semi-adiabatic calorimetry data. The heat capacity (C_p) data between 273 and 400 K were fitted to a Maier-Kelley polynomial C_p(T in K)=280.6 + 0.6149T–3199700T^–2. The Gibbs free energy of formation is –3162.2 ± 4.6 kJ mol^–1. Speciation and activity calculations for Fe(III)–SO₄ solutions show that these new thermodynamic data reproduce the results of solubility experiments with hydronium jarosite. A spin-glass freezing transition was manifested as a broad anomaly in the C_p data, and as a broad maximum in the zero-field-cooled magnetic susceptibility data at 16.5 K. Another anomaly in C_p, below 0.7 K, has been tentatively attributed to spin cluster tunneling. A set of thermodynamic values for an ideal composition end member (H₃O)Fe₃(SO₄)₂(OH)₆ was estimated: G^o_f= –3226.4 ± 4.6 kJ mol^–1, H^o_f=–3770.2 ± 4.6 kJ mol^–1, S^o=448.2 ± 0.7 J mol^–1 K^–1, C_p (T in K)=287.2 + 0.6281T–3286000T^–2 (between 273 and 400 K).     

Oxyvanite,V<Subscript>3</Subscript>O<Subscript>5</Subscript>, a new mineral species and the oxyvanite-berdesinskiite V<Subscript>2</Subscript>TiO<Subscript>5</Subscript> series from metamorphic rocks of the Slyudyanka Complex,southern Baikal region

Oxyvanite has been identified as an accessory mineral in Cr-V-bearing quartz-diopside meta- morphic rocks of the Slyudyanka Complex in the southern Baikal region, Russia. The new mineral was named after constituents of its ideal formula (oxygen and vanadium). Quartz, Cr-V-bearing tremolite and micas, calcite, clinopyroxenes of the diopside-kosmochlor-natalyite series, Cr-bearing goldmanite, eskolaite-karelianite dravite-vanadiumdravite, V-bearing titanite, ilmenite, and rutile, berdesinskiite, schreyerite, plagioclase, scapolite, barite, zircon, and unnamed U-Ti-V-Cr phases are associated minerals. Oxyvanite occurs as anhedral grains up to 0.1–0.15 mm in size, without visible cleavage and parting. The new mineral is brittle, with conchoidal fracture. Observed by the naked eye, the mineral is black, with black streak and resinous luster. The microhardness (VHN) is 1064–1266 kg/mm² (load 30 g), and the mean value is 1180 kg/mm². The Mohs hardness is about 7.0–7.5. The calculated density is 4.66(2) g/cm³. The color of oxyvanite is pale cream in reflected light, without internal reflections. The measured reflectance in air is as follows (λ, nm-R, %): 440-17.8; 460-18; 480-18.2; 520-18.6; 520-18.6; 540-18.8; 560-18.9; 580-19; 600-19.1; 620-19.2; 640-19.3; 660-19.4; 680-19.5; 700-19.7. Oxyvanite is monoclinic, space group C2/c; the unit-cell dimensions are a = 10.03(2), b = 5.050(1), c = 7.000(1) Å, β = 111.14(1)°, V = 330.76(5)ų, Z = 4. The strongest reflections in the X-ray powder pattern [d, Å, (I in 5-number scale)(hkl)] are 3.28 (5) (20\(\bar 2\)); 2.88 (5) (11\(\bar 2\)); 2.65, (5) (310); 2.44 (5) (112); 1.717 (5) (42\(\bar 2\)); 1.633 (5) (31\(\bar 4\)); 1.446 (4) (33\(\bar 2\)); 1.379 (5) (422). The chemical composition (electron microprobe, average of six point analyses, wt %): 14.04 TiO₂, 73.13 V₂O₃ (53.97 V₂O_3calc, 21.25 VO_2calc), 10.76 Cr₂O₃, 0.04 Fe₂O₃, 0.01 Al₂O₃, 0.02 MgO, total is 100.03. The empirical formula is (V _1.70 ³⁺ Cr_0.30)_2.0(V _0.59 ⁴⁺ Ti_0.41)_1.0O₅. Oxyvanite is the end member of the oxyvanite-berdesinskiite series with homovalent isomorphic substitution of V⁴⁺ for Ti. The type material has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

Calorimetric study on high-pressure transitions in KAlSi<Subscript>3</Subscript>O<Subscript>8</Subscript>

KAlSi₃O₈ sanidine dissociates into a mixture of K₂Si₄O₉ wadeite, Al₂SiO₅ kyanite and SiO₂ coesite, which further recombine into KAlSi₃O₈ hollandite with increasing pressure. Enthalpies of KAlSi₃O₈ sanidine and hollandite, K₂Si₄O₉ wadeite and Al₂SiO₅ kyanite were measured by high-temperature solution calorimetry. Using the data, enthalpies of transitions at 298 K were obtained as 65.1 ± 7.4 kJ mol^–1 for sanidine wadeite + kyanite + coesite and 99.3 ± 3.6 kJ mol^–1 for wadeite + kyanite + coesite hollandite. The isobaric heat capacity of KAlSi₃O₈ hollandite was measured at 160–700 K by differential scanning calorimetry, and was also calculated using the Kieffer model. Combination of both the results yielded a heat-capacity equation of KAlSi₃O₈ hollandite above 298 K as C_p=3.896 × 10²–1.823 × 10³T^–0.5–1.293 × 10⁷T^–2+1.631 × 10⁹T^–3 (C_p in J mol^–1 K^–1, T in K). The equilibrium transition boundaries were calculated using these new data on the transition enthalpies and heat capacity. The calculated transition boundaries are in general agreement with the phase relations experimentally determined previously. The calculated boundary for wadeite + kyanite + coesite hollandite intersects with the coesite–stishovite transition boundary, resulting in a stability field of the assemblage of wadeite + kyanite + stishovite below about 1273 K at about 8 GPa. Some phase–equilibrium experiments in the present study confirmed that sanidine transforms directly to wadeite + kyanite + coesite at 1373 K at about 6.3 GPa, without an intervening stability field of KAlSiO₄ kalsilite + coesite which was previously suggested. The transition boundaries in KAlSi₃O₈ determined in this study put some constraints on the stability range of KAlSi₃O₈ hollandite in the mantle and that of sanidine inclusions in kimberlitic diamonds.     

Pressure induced phase transition in Pb<Subscript>6</Subscript>Bi<Subscript>2</Subscript>S<Subscript>9</Subscript>

The crystal structure of Pb₆Bi₂S₉ is investigated at pressures between 0 and 5.6 GPa with X-ray diffraction on single-crystals. The pressure is applied using diamond anvil cells. Heyrovskyite (Bbmm, a = 13.719(4) Å, b = 31.393(9) Å, c = 4.1319(10) Å, Z = 4) is the stable phase of Pb₆Bi₂S₉ at ambient conditions and is built from distorted moduli of PbS-archetype structure with a low stereochemical activity of the Pb²⁺ and Bi³⁺ lone electron pairs. Heyrovskyite is stable until at least 3.9 GPa and a first-order phase transition occurs between 3.9 and 4.8 GPa. A single-crystal is retained after the reversible phase transition despite an anisotropic contraction of the unit cell and a volume decrease of 4.2%. The crystal structure of the high pressure phase, β-Pb₆Bi₂S₉, is solved in Pna2 ₁ (a = 25.302(7) Å, b = 30.819(9) Å, c = 4.0640(13) Å, Z = 8) from synchrotron data at 5.06 GPa. This structure consists of two types of moduli with SnS/TlI-archetype structure in which the Pb and Bi lone pairs are strongly expressed. The mechanism of the phase transition is described in detail and the results are compared to the closely related phase transition in Pb₃Bi₂S₆ (lillianite).     

Batisivite,V<Subscript>8</Subscript>Ti<Subscript>6</Subscript>[Ba(Si<Subscript>2</Subscript>O)]O<Subscript>28</Subscript>, a new mineral species from the derbylite group

Batisivite has been found as an accessory mineral in the Cr-V-bearing quartz-diopside metamorphic rocks of the Slyudyanka Complex in the southern Baikal region, Russia. A new mineral was named after the major cations in its ideal formula (Ba, Ti, Si, V). Associated minerals are quartz, Cr-V-bearing diopside and tremolite; calcite; schreyerite; berdesinskiite; ankangite; V-bearing titanite; minerals of the chromite-coulsonite, eskolaite-karelianite, dravite-vanadiumdravite, and chernykhite-roscoelite series; uraninite; Cr-bearing goldmanite; albite; barite; zircon; and unnamed U-Ti-V-Cr phases. Batisivite occurs as anhedral grains up to 0.15–0.20 mm in size, without visible cleavage and parting. The new mineral is brittle, with conchoidal fracture. Observed by the naked eye, the mineral is black and opaque, with a black streak and resinous luster. Batisivite is white in reflected light. The microhardness (VHN) is 1220–1470 kg/mm² (load is 30 g), the mean value is 1330 kg/mm². The Mohs hardness is near 7. The calculated density is 4.62 g/cm³. The new mineral is weakly anisotropic and bireflected. The measured values of reflectance are as follows (λ, nm—R _max ^′ /R _min ^′ ): 440—17.5/17.0; 460—17.3/16.7; 480—17.1/16.5; 500—17.2/16.6; 520—17.3/16.7; 540—17.4/16.8; 560—17.5/16.8; 580—17.6/16.9; 600—17.7/17.1; 620—17.7/17.1; 640—17.8/17.1; 660—17.9/17.2; 680—18.0/17.3; 700—18.1/17.4. Batisivite is triclinic, space group P \(\overline 1\); the unit-cell dimensions are: a = 7.521(1) Å, b = 7.643(1) Å, c = 9.572(1) Å, α = 110.20°(1), β = 103.34°(1), γ = 98.28°(1), V = 487.14(7) ų, Z = 1. The strongest reflections in the X-ray powder diffraction pattern [d, Å (I, %)(hkl)] are: 3.09(8)(12\(\overline 2\)); 2.84, 2.85(10)(021, 120); 2.64(8)(21\(\overline 3\)); 2.12(8)(31\(\overline 3\)); 1.785(8)(32\(\overline 4\)), 1.581(10)(24\(\overline 2\)); 1.432, 1.433(10)(322, 124). The chemical composition (electron microprobe, average of 237 point analyses, wt %) is: 0.26 Nb₂O₅, 6.16 SiO₂, 31.76 TiO₂, 1.81 Al₂O₃, 8.20 VO₂, 26.27 V₂O₃, 12.29 Cr₂O₃, 1.48 Fe₂O₃, 0.08 MgO, 11.42 BaO; the total is 99.73. The VO₂/V₂O₃ ratio has been calculated. The simplified empirical formula is (V _4.8 ³⁺ Cr_2.2V _0.7 ⁴⁺ Fe_0.3)_8.0(Ti_5.4V _0.6 ⁴⁺ )_6.0[Ba(Si_1.4Al_0.5O_0.9)]O₂₈. An alternative to the title formula could be a variety (with the diorthogroup Si₂O₇) V₈Ti₆[Ba(Si₂O₇)]O₂₂. Batisivite probably pertains to the V ₈ ³⁺ Ti ₆ ⁴⁺ [Ba(Si₂O)]O₂₈-Cr ₈ ³⁺ Ti ₆ ⁴⁺ [Ba(Si₂O)]O₂₈ solid solution series. The type material of batisivite has been deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

A 50-year record of NO<Subscript>x</Subscript> and SO<Subscript>2</Subscript> sources in precipitation in the Northern Rocky Mountains,USA

Ice-core samples from Upper Fremont Glacier (UFG), Wyoming, were used as proxy records for the chemical composition of atmospheric deposition. Results of analysis of the ice-core samples for stable isotopes of nitrogen (δ¹⁵N, ) and sulfur (δ³⁴S, ), as well as and deposition rates from the late-1940s thru the early-1990s, were used to enhance and extend existing National Atmospheric Deposition Program/National Trends Network (NADP/NTN) data in western Wyoming. The most enriched δ³⁴S value in the UFG ice-core samples coincided with snow deposited during the 1980 eruption of Mt. St. Helens, Washington. The remaining δ³⁴S values were similar to the isotopic composition of coal from southern Wyoming. The δ¹⁵N values in ice-core samples representing a similar period of snow deposition were negative, ranging from -5.9 to -3.2 ‰ and all fall within the δ¹⁵N values expected from vehicle emissions. Ice-core nitrate and sulfate deposition data reflect the sharply increasing U.S. emissions data from 1950 to the mid-1970s.     

The crystal structure of alumoklyuchevskite,K<Subscript>3</Subscript>Cu<Subscript>3</Subscript>AlO<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript>

The crystal structure of the unstable mineral alumoklyuchevskite K₃Cu₃AlO₂(SO₄)₄ [monoclinic, I2, a = 18.772(7), b = 4.967(2), c = 18.468(7) Å, β = 101.66(1)°, V = 1686(1) Å] was refined to R ₁ = 0.131 for 2450 unique reflections with F ≥ 4σF _hkl. The structure is based on oxocentered tetrahedrons (OAlCu ₃ ⁷⁺ ) linked into chains via edges. Each chain is surrounded by SO₄ tetrahedrons forming a structural complex. Each complex is elongated along the b axis. This type of crystal structure was also found in other fumarole minerals of the Great Tolbachik Fissure Eruption (GTFE, Kamchatka Peninsula, Russia, 1975–1976), klyuchevskite, K₃Cu₃Fe³⁺O₂(SO₄)₄; and piypite, K₂Cu₂O(SO₄)₂.     

Equation of state,structural behaviour and phase diagram of synthetic MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as a function of pressure and temperature

The behaviour of synthetic Mg-ferrite (MgFe₂O₄) has been investigated at high pressure (in situ high-pressure synchrotron radiation powder diffraction at ESRF) and at high temperature (in situ high-temperature X-ray powder diffraction) conditions. The elastic properties determined by the third-order Birch–Murnaghan equation of state result in K₀=181.5(± 1.3) GPa, K=6.32(± 0.14) and K= –0.0638 GPa^–1. The symmetry-independent coordinate of oxygen does not show significant sensitivity to pressure, and the structure shrinking is mainly attributable to the shortening of the cell edge (homogeneous strain). The lattice parameter thermal expansion is described by _a0+_a1*(T–298)+_a2/(T–298)², where _a0=9.1(1) 10^–6 K^–1, _a1=4.9(2) 10^–9 K^–2 and _a2= 5.1(5) 10^–2 K. The high-temperature cation-ordering reaction which MgFe-spinel undergoes has been interpreted by the ONeill model, whose parameters are = 22.2(± 1.8) kJ mol^–1 and =–17.6(± 1.2) kJ mol^–1. The elastic and thermal properties measured have then been used to model the phase diagram of MgFe₂O₄, which shows that the high-pressure transition from spinel to orthorombic CaMn₂O₄-like structure at T < 1700 K is preceded by a decomposition into MgO and Fe₂O₃.     

New density measurements on carbonate liquids and the partial molar volume of the CaCO<Subscript>3</Subscript> component

Density measurements on nine liquids in the CaCO₃–Li₂CO₃–Na₂CO₃–K₂CO₃ quaternary system were performed at 1 bar between 555 and 969 °C using the double-bob Archimedean method. Our density data on the end-member alkali carbonate liquids are in excellent agreement with the NIST standards compiled by Janz (1992). The results were fitted to a volume equation that is linear in composition and temperature; this model recovers the measured volumes within experimental error (±0.18% on average, with a maximum residual of ±0.50%). Our results indicate that the density of the CaCO₃ component in natrocarbonate liquids is 2.502 (±0.014) g/cm³ at 800 °C and 1 bar, which is within the range of silicate melts; its coefficient of thermal expansion is 1.8 (±0.5)×10^–4 K^–1 at 800 °C. Although the volumes of carbonate liquids mix linearly with respect to carbonate components, they do not mix linearly with silicate liquids. Our data are used with those in the literature to estimate the value of in alkaline silicate magmas (20 cm³/mol at 1400 °C and 20 kbar), where CO₂ is dissolved as carbonate in close association with Ca. Our volume measurements are combined with sound speed data in the literature to derive the compressibility of the end-member liquids Li₂CO₃, Na₂CO₃, and K₂CO₃. These results are combined with calorimetric data to calculate the fusion curves for Li₂CO₃, Na₂CO₃, and K₂CO₃ to 5 kbar; the calculations are in excellent agreement with experimental determinations of the respective melting reactions.Editorial responsibility: I Carmichael     

Hydroxylborite,Mg<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)(OH)<Subscript>3</Subscript>, a new mineral species and isomorphous series fluoborite-hydroxylborite

Hydroxylborite, a new mineral species, an analogue of fluoborite with OH > F, has been found at the Titovsky deposit (57°41′N, 125°22′E), the Chersky Range, Dogdo Basin, Sakha-Yakutia Republic, Russia. Prismatic crystals of the new mineral are dominated by the {10\(\overline 1 \)0} faces without distinct end forms and reach (1?1.5) × (0.1?0.2) mm in size. Radial aggregates of such crystals occur in the mineralized marble adjacent to the boron ore (suanite-kotoite-ludwigite). Calcite, dolomite, Mg-rich ludwigite, kotoite, szaibelyite, clinohumite, magnetite, serpentine, and chlorite are associated minerals. Hydroxylborite is transparent colorless, with a white streak and vitreous luster. The new mineral is brittle. The Mohs’ hardness is 3.5. The cleavage is imperfect on {0001}. The density measured with equilibration in heavy liquids is 2.89(1) g/cm³; the calculated density is 2.872 g/cm³. The wave numbers of the absorption bands in the IR spectrum of hydroxylborite are (cm^?1; sh is shoulder): 3668, 1233, 824, 742, 630sh, 555sh, 450sh, and 407. The new mineral is optically uniaxial, negative, ω = 1.566(1), and ε = 1.531(1). The chemical composition (electron microprobe, H₂O measured with the Penfield method, wt %) is 18.43 B₂O₃, 65.71 MgO, 10.23 F, 9.73 H₂O, 4.31-O = F₂, where the total is 99.79. The empirical formula calculated on the basis of 6 anions pfu is as follows: Mg_3.03B_0.98[(OH)_2.00F_1.00]O_3.00. Hydroxylborite is hexagonal, and the space group is P6₃/m. The unit-cell dimensions are: a = 8.912(8) Å, c = 3.112(4) Å, V = 214.05(26) ų, and Z = 2. The strongest reflections in the X-ray powder pattern [d, Å (I, %)(hkil)] are: 7.69(52)(01\(\overline 1 \)0), 4.45(82)(11\(\overline 2 \)0), 2.573(65)(03\(\overline 3 \)0), 2.422(100)(02\(\overline 2 \)1), and 2.128(60)(12\(\overline 3 \)1). The compatibility index 1 ? (K _p/K _c) is 0.038 (excellent) for the calculated density and 0.044 (good) for the measured density. The type material of hydroxylborite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow (inventory number 91968) and the Geological Museum of the All-Russia Institute of Mineral Resources, Moscow (inventory number M-1663).     

An infrared and <Superscript>1</Superscript>H MAS NMR investigation of strong hydrogen bonding in ussingite,Na<Subscript>2</Subscript>AlSi<Subscript>3</Subscript>O<Subscript>8</Subscript>(OH)

The mineral ussingite, Na₂AlSi₃O₈(OH), an interrupted tectosilicate, has strong hydrogen bonding between OH and the other nonbridging oxygen atom in the structure. Infrared spectra contain a strongly polarized, very broad OH-stretching band with an ill-defined maximum between 1500 and 1800 cm^–1, and a possible OH librational bending mode at 1295 cm^–1. The IR spectra confirm the orientation of the OH vector within the triclinic unit cell as determined from X-ray refinement (Rossi et al. 1974). There are three distinct bands in the ¹H NMR spectrum of ussingite: a predominant band at 13.5 ppm (TMS) representing 90% of the structural hydrogen, a second band at 15.9 ppm corresponding to 8% of the protons, and a third band at 11.0 ppm accounting for the remaining 2% of structural hydrogen. From the correlation between hydrogen bond length and ¹H NMR chemical shift (Sternberg and Brunner 1994), the predominant hydrogen bond length (H...O) was calculated to be 1.49 Å, in comparison to the hydrogen bond length determined from X-ray refinement (1.54 Å). The population of protons at 15.9 ppm is consistent with 5–8% Al–Si disorder. Although the ussingite crystal structure and composition are similar to those of low albite, the bonding environment of OH in low albite and other feldspars, as characterized through IR and ¹H NMR, is fundamentally different from the strong hydrogen bonding found in ussingite.     

Zinclipscombite,ZnFe<Stack><Subscript>2</Subscript><Superscript>3+</Superscript></Stack>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>, a new mineral species

Zinclipscombite, a new mineral species, has been found together with apophyllite, quartz, barite, jarosite, plumbojarosite, turquoise, and calcite at the Silver Coin mine, Edna Mountains, Valmy, Humboldt County, Nevada, United States. The new mineral forms spheroidal, fibrous segregations; the thickness of the fibers, which extend along the c axis, reaches 20 μm, and the diameter of spherulites is up to 2.5 mm. The color is dark green to brown with a light green to beige streak and a vitreous luster. The mineral is translucent. The Mohs hardness is 5. Zinclipscombite is brittle; cleavage is not observed; fracture is uneven. The density is 3.65(4) g/cm³ measured by hydrostatic weighing and 3.727 g/cm³ calculated from X-ray powder data. The frequencies of absorption bands in the infrared spectrum of zinclipscombite are (cm^?1; the frequencies of the strongest bands are underlined; sh, shoulder; w, weak band) 3535, 3330sh, 3260, 1625w, 1530w, 1068, 1047, 1022, 970sh, 768w, 684w, 609, 502, and 460. The Mössbauer spectrum of zinclipscombite contains only a doublet corresponding to Fe³⁺ with sixfold coordination and a quadrupole splitting of 0.562 mm/s; Fe²⁺ is absent. The mineral is optically uniaxial and positive, ω = 1.755(5), ? = 1.795(5). Zinclipscombite is pleochroic, from bright green to blue-green on X and light greenish brown on Z (X > Z). Chemical composition (electron microprobe, average of five point analyses, wt %): CaO 0.30, ZnO 15.90, Al₂O₃ 4.77, Fe₂O₃ 35.14, P₂O₅ 33.86, As₂O₅ 4.05, H₂O (determined by the Penfield method) 4.94, total 98.96. The empirical formula calculated on the basis of (PO₄,AsO₄)₂ is (Zn_0.76Ca_0.02)_Σ0.78(Fe _1.72 ³⁺ Al_0.36)_Σ2.08[(PO₄)_1.86(AsO₄)_0.14]_Σ2.00(OH)_{1. 80} · 0.17H₂O. The simplified formula is ZnFe ₂ ³⁺ (PO₄)₂(OH)₂. Zinclipscombite is tetragonal, space group P4₃2₁2 or P4₁2₁2; a = 7.242(2) Å, c = 13.125(5) Å, V = 688.4(5) ų, Z = 4. The strongest reflections in the X-ray powder diffraction pattern (d, (I, %) ((hkl)) are 4.79(80)(111), 3.32(100)(113), 3.21(60)(210), 2.602(45)(213), 2.299(40)(214), 2.049(40)(106), 1.663(45)(226), 1.605(50)(421, 108). Zinclipscombite is an analogue of lipscombite, Fe²⁺Fe ₂ ³⁺ (PO₄)₂(OH)₂ (tetragonal), with Zn instead of Fe²⁺. The mineral is named for its chemical composition, the Zn-dominant analogue of lipscombite. The type material of zinclipscombite is deposited in the Mineralogical Collection of the Technische Universität Bergakademie Freiberg, Germany.     

Invasion of anthropogenic CO<Subscript>2</Subscript> recorded in planktonic foraminifera from the northern Gulf of Aqaba

The stable carbon isotopic composition of the planktonic foraminifera Globigerinoides sacculifer and G. ruber (white) and sedimentary organic matter from the northern Gulf of Aqaba have been investigated to estimate changes in ¹³C_DIC in surface waters during the last 1,000 years. The high sedimentation rates at the core sites (about 54 cm/Kyear) provide high temporal resolution (~10 years). Recent sediments at the top of the cores reflect conditions younger than 1950. The ¹³C records of the planktonic foraminifera from three multicores display similar trends, showing a uniform and consistent pattern before the 1750s, and a gradual decrease of approximately 0.63 over the last two centuries. This decrease seems to track the decrease of ¹³C_DIC in surface waters, which is mainly caused by the increase of anthropogenic input of ¹³C-depleted CO₂ into the atmosphere. Similarly, a trend towards lighter values of the carbon isotopic composition of sedimentary organic matter (¹³C_org) during the last 200 years supports the interpretation obtained from the planktonic foraminiferal ¹³C. Furthermore, direct measurements of seawater show that ¹³C of the dissolved inorganic carbon (DIC) in the northern Gulf of Aqaba has decreased by about 0.44 during the period 1979–2000. The average annual decrease is 0.021, which is similar to that observed globally. The ¹³C values of planktonic foraminifera combined with organic matter ¹³C from marine sediments are good indicators for reconstructing past changes in atmospheric CO₂ concentrations from the northern Gulf of Aqaba.     

Crystal chemistry of selenates with mineral-like structures: VIII. Butlerite chains in the structure of K(UO<Subscript>2</Subscript>)(SeO<Subscript>4</Subscript>)(OH)(H<Subscript>2</Subscript>O)

A new potassium uranyl selenate compound K(UO₂)(SeO₄)(OH)(H₂O) has been synthesized for the first time using the technique of evaporation from water solution. Its crystal structure has been solved by direct methods (monoclinic, P2₁/c,a = 8.0413(9) Å, b = 8.0362(9) Å, c = 11.6032(14) Å, β = 106.925(2)°, V = 717.34(14) ų) and refined to R ₁ = 0.0319 (wR ₂ = 0.0824) for 1285 reflections with |F ₀| > 4σ _F . The structure consists of [(UO₂(SeO₄)(OH)(H₂O)]^? chains extending along axis b. In the chains, the uranyl pentagonal bipyramids are linked via bridged hydroxyl anions and tetrahedral oxoanions [SeO₄]^2?. Potassium ions are situated between these chains. No chains of that type have been observed in uranyl compounds earlier, but they had been detected in the structures of butlerite, parabutlerite, uklonskovite, fibroferrite, and a number of synthetic compounds.     

Elastic behavior of vanadinite,Pb<Subscript>10</Subscript>(VO<Subscript>4</Subscript>)<Subscript>6</Subscript>Cl<Subscript>2</Subscript>, a microporous non-zeolitic mineral

The high-pressure behavior of a vanadinite (Pb₁₀(VO₄)₆Cl₂, a = b = 10.3254(5), c = 7.3450(4) Å, space group P6₃/m), a natural microporous mineral, has been investigated using in-situ HP-synchrotron X-ray powder diffraction up to 7.67 GPa with a diamond anvil cell under hydrostatic conditions. No phase transition has been observed within the pressure range investigated. Axial and volume isothermal Equations of State (EoS) of vanadinite were determined. Fitting the P–V data with a third-order Birch-Murnaghan (BM) EoS, using the data weighted by the uncertainties in P and V, we obtained: V ₀ = 681(1) Å³, K ₀ = 41(5) GPa, and K′ = 12.5(2.5). The evolution of the lattice constants with P shows a strong anisotropic compression pattern. The axial bulk moduli were calculated with a third-order “linearized” BM-EoS. The EoS parameters are: a ₀ = 10.3302(2) Å, K ₀(a) = 35(2) GPa and K′(a) = 10(1) for the a-axis; c ₀ = 7.3520(3) Å, K ₀(c) = 98(4) GPa, and K′(c) = 9(2) for the c-axis (K ₀(a):K ₀(c) = 1:2.80). Axial and volume Eulerian-finite strain (fe) at different normalized stress (Fe) were calculated. The weighted linear regression through the data points yields the following intercept values: Fe _a (0) = 35(2) GPa for the a-axis, Fe _c (0) = 98(4) GPa for the c-axis and Fe _V (0) = 45(2) GPa for the unit-cell volume. The slope of the regression lines gives rise to K′ values of 10(1) for the a-axis, 9(2) for the c-axis and 11(1) for the unit cell-volume. A comparison between the HP-elastic response of vanadinite and the iso-structural apatite is carried out. The possible reasons of the elastic anisotropy are discussed.     

Crystal chemistry of natural and synthetic lead oxyhalides. Part I. Crystal structure of Pb<Subscript>13</Subscript>O<Subscript>10</Subscript>Cl<Subscript>6</Subscript>

Crystals of lead oxychloride Pb₁₃O₁₀Cl₆ have been synthesized on the basis of high-temperature solid-state reactions. The Pb₁₃O₁₀Cl₆ structure was studied using X-ray single-crystal diffraction analysis. The compound is monoclinic, and the space group is C2/c; the unit-cell dimensions are a = 16.1699(14), b = 7.0086(6), c = 23.578(2) Å, β = 97.75°, and V = 2647.6(4) ų. The structure has been solved by direct methods and refined to R ₁ = 0.0505 for 2671 observed unique reflections. The structure is a 3D framework consisting of OPb₄ tetrahedrons. Chlorine atoms are located in the framework channels. The structure contains seven symmetrically independent Pb atoms, which are coordinated by 2 to 4 O^2? and 2 to 4 Cl^? anions. The synthesized compound is compared with other natural and synthetic lead oxyhalides.