Dielectric constants of tephroite,fayalite and olivine and the oxide additivity rule

The dielectric constants and dissipation factors of synthetic tephroite (Mn₂SiO₄), fayalite (Fe₃SiO₄) and a forsteritic olivine (Mg_1.80Fe_0.22SiO₄) were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: tephroite, κ′_a= 8.79 tan δ_a = 0.0006 κ′_b = 10.20 tan δ_b = 0.0006 κ′_c= 8.94 tan δ_c= 0.0008 fayalite, gk′_a = 8.80 tan δ_a = 0.0004 gk′_b= 8.92 tan δ_b = 0.0018 gk′_c = 8.58 tan δ_c = 0.0010 olivine, gk′_a = 7.16 tan δ_a = 0.0006 gk′_b = 7.61 tan δ_b = 0.0008 gk′_c = 7.03 tan δ_c = 0.0006 The low dielectric constant and loss of the fayalite indicate an exceptionally low Fe³⁺ content. An FeO polarizability of 4.18 ų, determined from α_D(FeO) = [α_D (Fe₂SiO₄)-α_D(SiO₂)]/2, is probably a more reliable value for stoichiometric FeO than could be obtained from Fe_xO where x = 0.90–0.95. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to α_D(M₂M′X₂) = 2α_D(MX) + α_D(M′X₂) is ～+2.8% for tephroite and +0.2% for olivine. The deviation from additivity in tephroite is discussed.     

Dielectric constants of apatite,epidote, vesuvianite,and zoisite,and the oxide additivity rule

The dielectric constants and dielectric loss values of 4 Ca-containing minerals were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: vesuvianitel κ′ _a=9.93 tan δ=0.006 κ′ _c=9.79 tan δ=0.005 vesuvianitel κ′ _a=10.02 tan δ=0.002 κ′ _c=9.85 tan δ=0.003 zoisite1 κ′ _a =10.49 tan δ=0.0006 κ′ _b =15.31 tan δ=0.0008 κ′ _c=9.51 tan δ=0.0008 zoisite2 κ′ _a =10.55 tan δ=0.0011 κ′ _b =15.45 tan δ=0.0013 κ′ _c=9.39 tan δ=0.0008 epidote κ′ ₁₁= 9.52 tan δ=0.0008 κ′ ₂₂=17.1 tan δ=0.0009 κ′ ₃₃= 9.37 tan δ=0.0006 fluorapatite1 κ′ _a =10.48 tan δ=0.0008 κ′ _c = 8.72 tan δ=0.0114 fluorapatite2 κ′ _a =10.40 tan δ=0.0010 κ′ _c=8.26 tan δ=0.0178 The deviation (δ) between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to α _D (mineral)=∑ α _D (oxides) for vesuvianite is ～ 0.5%. The large deviations of epidote and zoisite from the additivity rule with Δ=+ 10.1 and + 11.7%, respectively, are attributed to “rattling” Ca ions. The combined effects of both a large F thermal parameter and possible F-ion conductivity in fluorapatite are believed to be responsible for Δ=+2–3%. Although variation of oxygen polarizability with oxygen molar volume (V_o) is believed to affect the total polarizabilities, the variation of V_o in these Ca minerals is too small to observe the effect.     

Dielectric constants of topaz,orthoclase and scapolite and the oxide additivity rule

The dielectric constants and dissipation factors of topaz, scapolite and orthoclase were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: topaz κ′ _a =6.61 tan δ=0.0005 κ′ _b =6.82 tan δ=0.0007 κ′ _c =6.81 tan δ=0.0007 orthoclase κ′ _a =4.69 tan δ=0.0007 κ′ _b =5.79 tan δ=0.0007 κ′ _c =5.63 tan δ=0.0011 κ′ ₁₁ =4.72 κ′ ₂₂ =5.79 κ′ ₃₃ =5.76 scapolite κ′ _a =6.74 tan δ=0.0004 κ′ _c =8.51 tan δ=0.0004 The deviation (Δ) between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of ion polarizabilities according to α _D (mineral)=∑α_D (ions) for topaz is 2.5%. The large deviations of orthoclase and scapolite from the oxide additivity rule with δ=+7.2 and + 17.6%, respectively, are attributed to “rattling” K ions in orthoclase and “rattling” (Na,K,Ca) ions and disordered O⁼ and Cl^- ions in scapolite.     

Ab initio calculations on the O<Subscript>2</Subscript><Superscript>3−</Superscript>-Y<Superscript>3+</Superscript> center in CaF<Subscript>2</Subscript> and SrF<Subscript>2</Subscript>: its electronic structure and hyperfine constants

The O₂ ^3?-Y³⁺ center in fluorite-type structures (CaF₂ and SrF₂) has been investigated at the density functional theory (DFT) level using the CRYSTAL06 code. Our calculations were performed by means of the hybrid B3PW method in which the Hartree–Fock exchange is mixed with the DFT exchange functional, using Becke’s three parameter method, combined with the non-local correlation functionals by Perdew and Wang. Our calculations confirm the stability and the molecular character of the O₂ ^3?-Y³⁺ center. The unpaired electron is shown to be almost exclusively localized on and equally distributed between the two oxygen atoms that are separated by a bond distance of 2.47 Å in CaF₂ and 2.57 Å in SrF₂. The calculated ¹⁷O and ¹⁹F hyperfine constants for of the O₂ ^3?-Y³⁺ center are in good agreement with their corresponding experimental values reported by previous electron paramagnetic resonance and electron nuclear double resonance studies, while discrepancies are notable for the ⁸⁹Y hyperfine constants.     

Heyrovskýite, 6(Pb0.86Bi0.08(Ag,Cu)0.04)S . Bi2S3 from Hůrky,Czechoslovakia, a new mineral of genetic interest

Heyrovskýite has a composition range from 6(Pb_0.83Bi_0.10(Ag, Cu)_0.07) S . Bi₂S₃ to 6(Pb_0.92Bi_0.05(Ag, Cu)_0.03) S . Bi₂S₃. It is orthorhombic. Crystal forms {100}, {010}, {120}, {140}, {250}, and {321} (?) were observed; {010} and {140} are dominant. Elongated c, flattened (010). a:b:c _morph=0.432:1:0.128. Cell parameters a=13.705±0.013 Å, b=31.194±0.033, c=4.121±0.003, a:b:c _X-ray=0.439:1:0.132. The diffraction symbol is Bb, compatible with Bbmm, Bb2₁ m, Bbm2. Morphology corresponds to point groups mmm or mm2, reducing the possible space groups to Bbmm and Bbm2. Density at 20 °C is 7.17 g/cm³, calculated, 7.18; Z=4. Micro-indentation hardness (VHN) (50 g load) is 166 to 234 kp/mm². Strongly anisotropic; reflectance strongly variable, roughly the same as of galena. Etch tests: HNO₃ (1:1) and HCl (1:1) positive, FeCl₃ 20%, HgCl₂ 5%, KCN 20%, and KOH 40% all negative. Powder data are identical with those for phase II of Otto and Strunz (1968). Heyrovskýite is associated with galena and cosalite at H?rky, Czechoslovakia.     

Phase transition of potassium sulfate,K2SO4 (II); dielectric constant and electrical conductivity

The phase transition of K₂SO₄ has been investigated by measurements of the dielectric constant and electrical conductivity, correlated with the structural point of view. Using single crystals, the temperature dependences of the dielectric constants and electrical conductivities were measured at frequencies of 0.3, 1, 3, and 5 MHz in the temperature range from 20° to 640 °C. Within this range, the dielectric constant does not reach a maximum, but near the phase-transition temperature at 587° C, the dielectric constant along the c axis shows a larger discontinuity than those along the a and b axes. The temperature dependence of the dielectric constant is consistent with the disordered structure of the high temperature form. Based on the parabolic increase of the dielectric constant in the temperature range from 582° to 587° C, it is likely that the phase transition propagates through an intermediate state. The electrical conductivity coefficients of K₂SO₄ increase with increasing temperature, exhibiting semiconducting character above the phase-transition temperature. In the high-temperature form, the electrical conductivity along the a axis exceeds that along the c axis. Since the electrical conductivity of K₂SO₄ is mainly ionic in character, the migration of K⁺ ions makes a major contribution to the conduction process.     

Synthetic Mn3+-kyanite and viridine, (Al2-xMn x 3+ ) SiO5, in the system Al2O3-MnO-MnO2-SiO2

Experiments on the join Al₂SiO₅-“Mn₂SiO₅” of the system Al₂O₃-SiO₂-MnO-MnO₂ in the pressure/temperature range 10–20 kb/900–1050° C with gem quality andalusite, Mn₂O₃, and high purity SiO₂ as starting materials and using /_O2-buffer techniques to preserve the Mn³⁺ oxidation state had following results: At 20 kb/1000°C orange-yellow kyanite mixed crystals are formed. The kyanite solid solubility is limited at about (Al_1.88Mn _0.12 ³⁺ )SiO₅ and, thus, equals approximately that on the join Al₂SiO₅-“Fe₂SiO₅” (Langer and Frentrup, 1973) indicating that there is no Jahn-Teller stabilisation of Mn³⁺ in the kyanite matrix. 5 mole % substitution causes the kyanite lattice constants a _o, b _o, c _o, and V _o to increase by 0.015, 0.009, 0.014 Å, and 1.6 ų, resp., while α, β, γ, remain unchanged. Between 10 and 18 kb/900°C, Mn³⁺-substituted, strongly pleochroitic (emeraldgreen-yellow) andalusite_ss (viridine) was obtained. At 15 kb/900°C, the viridine compositional range is about (Al_1.86Mn _0.14 ³⁺ )SiO₅-(Al_1.56Mn _0,44 ³⁺ )SiO₅. Thus, Al→Mn³⁺ substitutional degrees are appreciably higher in andalusite than in kyanite, proving a strong Jahn-Teller effect of Mn³⁺ in the andalusite structure, which stabilises this structure type at the expense of kyanite and sillimanite and, thus, enlarges its PT-stability range extremely. 17 mole % substitution cause the andalusite constants a _o, b _o, c _o, and V _o to increase by 0.118, 0.029, 0.047 Å and 9.4 ų, resp. At “Mn₂SiO₅”-contents smaller than about 7 mole %, viridine coexists with Mn-poor kyanite. At “Mn₂SiO₅”-concentrations higher than the maximum kyanite or viridine miscibility, braunite (tetragonal, ideal formula Mn²⁺Mn³⁺[O₈/Si0₄]), pyrolusite and SiO₂ were found to coexist with the Mn³⁺-saturated ky _ss or and _ss, respectively. In both cases, braunites were Al-substituted (about 1 Al for 1 Mn³⁺). Pure synthetic braunites had the lattice constants a _o 9.425, c _o, 18.700 Å, V _o 1661.1 ų (ideal compn.) and a _o 9.374, c _o 18.593 ų, V _o 1633.6 ų (1 Al for 1 Mn³⁺). Stable coexistence of the Mn²⁺-bearing phase braunite with the Mn⁴⁺-bearing phase pyrolusite was proved by runs in the limiting system MnO-MnO₂-SiO₂.     

Thermodynamic behaviour of the high-temperature P\bar 1{\text{-}}I\bar 1 phase transition along the CaAl2Si2O8–SrAl2Si2O8 join

In situ high-temperature synchrotron radiation powder diffraction patterns were taken from room temperature to T = 740°C from synthetic feldspars along the join CaAl₂Si₂O₈–SrAl₂Si₂O₈ (An–SrF). Three samples of composition An₉₅SrF₅, An₉₀SrF₁₀ and An₈₅SrF₁₅ were investigated, and the evolution of cell parameters with T was determined by Rietveld analysis of powder X-ray diffraction patterns. The high-temperature $P\bar 1{\text{-}}I\bar 1$ phase transition, previously observed with T _c = 241°C in anorthite, was found in An₉₅SrF₅, An₉₀SrF₁₀ and An₈₅SrF₁₅ feldspars at T _c = 233(5)°, 195(2)° and 174(2)°C respectively. The transition was revealed by the disappearance of critical reflections and variations in the rate of change of cell parameters with temperature. A significant, although small (between 0.0025 and 0.0012 at room temperature), spontaneous strain could be measured, allowing the thermodynamic behaviour of the transition to be modelled. A second-order trend for An₉₀SrF₁₀ and An₈₅SrF₁₅ [β = 0.504(7) and 0.505(7) respectively] or nearly second-order for An₉₅SrF₅[β = 0.458(4)] was observed in contrast with tricritical behaviour of end member anorthite. An extrapolation of the T _c versus composition to room temperature indicates that the critical composition for the $P\bar 1$ phase is An₆₀SrF₄₀.     

The compressibility of Fe- and Al-bearing phase D to 30 GPa

High-pressure in situ X-ray diffraction experiment of Fe- and Al-bearing phase D (Mg_0.89Fe_0.14Al_0.25Si_1.56H_2.93O₆) has been carried out to 30.5 GPa at room temperature using multianvil apparatus. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields values of V ₀ = 86.10 ± 0.05 ų; K ₀ = 136.5 ± 3.3 GPa and K′ = 6.32 ± 0.30. If K′ is fixed at 4.0 K ₀ = 157.0 ± 0.7 GPa, which is 6% smaller than Fe–Al free phase D reported previously. Analysis of axial compressibilities reveals that the c-axis is almost twice as compressible (K _c  = 93.6 ± 1.1 GPa) as the a-axis (K _a  = 173.8 ± 2.2 GPa). Above 25 GPa the c/a ratio becomes pressure independent. No compressibility anomalies related to the structural transitions of H-atoms were observed in the pressure range to 30 GPa. The density reduction of hydrated subducting slab would be significant if the modal amount of phase D exceeds 10%.     

Dielectric constants of crystalline and amorphous spodumene,anorthite and diopside and the oxide additivity rule

The dielectric constants and dissipation factors of LiAlSi₂O₆, CaAl₂Si₂O₈ and CaMgSi₂O₆ in both the crystalline (α-spodumene, anorthite, and diopside) and amorphous forms were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: spodumene κ′ ₁₁=7.30 tan δ= 0.0007 κ′₂₂=8.463 tan δ= 0.0002 κ′₃₃ =11.12 tan δ= 0.0007 anorthite κ′ _a ^*=5.47 tan δ= 0.0009 κ′_b ^*=8.76 tan δ= 0.0010 κ′_c ^*=7.19 tan δ= 0.0013 diopside κ′₁₁=9.69 tan δ= 0.0016 κ′₂₂ = 7.31 tan δ= 0.0007 κ′₃₃=7.29 tan δ= 0.00019 LiAlSi₂O₆ κ′=8.07 tan δ= 0.047 amorphous CaAl₂Si₂O₈ κ′=7.50 tan δ= 0.0024 amorphous CaMgSi₂O₆ κ′=8.89 tan δ= 0.0021 amorphous The dielectric properties of a spodumene glass, progressively crystallized at different conditions, were also determined. As the crystallization temperature was increased from 720 to 920° C, κ′ increased from 6.22 to 6.44. The dissipation factor, tan δ, remained constant at 0.020. Similarly, as the crystallization time at 750° C increased from 0.5 hr to 6.0 hr, κ′ increased from 6.28 to 6.35. The deviations of the measured dielectric polarizabilities as determined from the Clausius-Mosotti equation from those calculated from the sum of oxide polarizabilities according to α _D(mineral, glass) = σ α _D(oxides) are +7.4% for α-spodumene, +1.2% for diopside, and +28.0, +19.6 and +15.9% for amorphous spodumene, anorthitie and diopside compositions, respectively. Positive deviations in α-spodumene and anorthite are consistent with lower than normal apparent cation bond valence sums and are believed to be evidence for loosely bonded “rattling” Li and Ca ions. Diopside, with Ca and Mg ions having normal bond valence sums, exhibits no abnormal deviation from additivity. Larger positive deviations in amorphous SiO₂, LiAlSi₂O₆, CaAl₂Si₂O₈ and CaMgSi₂O₆ are postulated to arise from a combination of loosely bonded cations and disordered O⁼ ions where the oxygen dielectric polarizability increased from its normal value of 2.0 ų in well-behaved oxides to 2.2–3.0 Å₃ in the amorphous phases.     

Fluorite solubility in hydrous haplogranitic melts at 100 MPa

Fluorite is the most common fluoride mineral in magmatic silicic systems and its crystallization can moderate or buffer fluorine concentrations in these settings. We have experimentally determined fluorite solubility and speciation mechanisms in haplogranitic melts at 800–950 °C, 100 MPa and aqueous-fluid saturation. The starting haplogranite compositions: peraluminous (alumina saturation index, ASI = 1.2), subaluminous (ASI = 1.0) and peralkaline (ASI = 0.8) were variably doped with CaO or F₂O₋₁ in the form of stoichiometric mineral or glass mixtures. The solubility of fluorite along the fluorite–hydrous haplogranite binaries is low: 1.054 ± 0.085 wt.% CaF₂ (peralkaline), 0.822 ± 0.076 wt.% (subaluminous) and 1.92 ± 0.15 wt.% (peraluminous) at 800 °C, 100 MPa and 10 wt.% H₂O, and exhibits a minimum at ASI ∼ 1. Fluorite saturation isotherms are strongly hyperbolic in the CaO–F₂O₋₁ space, suggesting that fluorite saturation is controlled by the activity product of CaO and F₂O₋₁, i.e., these components are partially decoupled in the melt structure. The form of fluorite liquidus isotherms implies distinct roles of fluorite crystallization: in Ca-dominant systems, fluorite crystallization is controlled by the fluorine concentration in the melt only and remains nearly independent of calcium contents; in F-rich systems, the crystallization of fluorite is determined by CaO contents and it does not buffer fluorine concentration in the melt. The apparent equilibrium constant, K, for the equilibrium CaO + cF₂O₋₁ = CaF₂ (+ associates) is log K= − (2.449 ± 0.085)·Al₂O₃^exc + (4.902 ± 0.066); the reaction-stoichiometry parameter varies as follows: c= − (0.92 ± 0.11)·Al₂O₃^exc + (1.042 ± 0.084) at 800 °C, 100 MPa and fluid saturation where Al₂O₃^exc are molar percent alumina in excess over alkali oxides. The reaction stoichiometry, c, changes at subaluminous composition: in peralkaline melts, competition of other network modifiers for excess fluorine anions leads to the preferential alkali–F short-range order, whereas in peraluminous compositions, excess alumina associates with calcium cations to form calcioaluminate tetrahedra. The temperature dependence of fluorite solubility is described by the binary symmetric Margules parameter, W = 36.0 ± 1.4 kJ (peralkaline), 39.7 ± 0.5 kJ (subaluminous) and 32.8 ± 0.7 kJ (peraluminous). The strong positive deviations from ideal mixing imply the occurrence of CaF₂–granite liquid–liquid immiscibility at temperatures above 1258 °C, which is consistent with previous experimental data. These experimental results suggest very low solubilities of fluorite in Ca-rich melts, consistent with the lack of fluorine enrichment in peralkaline rhyolites and calc-alkaline batholiths. On the other hand, high CaO concentrations necessary to crystallize fluorite in F-rich peraluminous melts are not observed in nature and thus magmatic crystallization of fluorite in topaz-bearing silicic suites is suppressed. A procedure for calculating fluorite solubility and the liquidus isotherms for a whole-rock composition and temperature of interest is provided.     

Ertixiite—a new mineral from the Altay Pegmatite Mine,Xinjiang, China

Ertixiite (Na₂Si₄O₉), a new mineral found in a miarolitic cavity of the Altay Pegmatite Mine, Xinjiang, China, is associated with topaz, apatite, quartz, cleavelandite, etc. The mineral is white, granular, and transparent. HNV=570.08?850.96 kg/mm² (Moh’s 5.8?6.5), D=2.35, N=1.502. Cubic system,a=5.975 Å, V=213.311 Å, Z=1,D _x =2.34g/cm³. The chemical composition of ertixiite (the average of six samples) is: Na₂O 17.97, CaO 2.82, SiO₂ 77.86, Al₂O₃ 1.45, FeO 0.05, total 100.15. The strongest lines in the X-ray powder pattern are 3.443(2, 111), 2.647(2. 210), 2.674(2,210), 1.996(8,221), 1.798(10,311), and 1.492(2,400).     

Elastic behavior and pressure-induced structure evolution of topaz up to 45 GPa

The behavior of a natural topaz, Al_2.00Si_1.05O_4.00(OH_0.26F_1.75), has been investigated by means of in situ single-crystal synchrotron X-ray diffraction up to 45 GPa. No phase transition or change in the compressional regime has been observed within the pressure-range investigated. The compressional behavior was described with a third-order Birch–Murnaghan equation of state (III-BM-EoS). The III-BM-EoS parameters, simultaneously refined using the data weighted by the uncertainties in P and V, are as follows: K _V = 158(4) GPa and K _V ′ = 3.3(3). The confidence ellipse at 68.3 % (Δχ² = 2.30, 1σ) was calculated starting from the variance–covariance matrix of K _V and K′ obtained from the III-BM-EoS least-square procedure. The ellipse is elongated with a negative slope, indicating a negative correlation of the parameters K _V and K _V ′, with K _V = 158 ± 6 GPa and K _V ′ = 3.3 ± 4. A linearized III-BM-EoS was used to obtain the axial-EoS parameters (at room-P), yielding: K(a) = 146(5) GPa [β _a = 1/(3K(a)) = 0.00228(6) GPa^?1] and K′(a) = 4.6(3) for the a-axis; K(b) = 220(4) GPa [β _b = 0.00152(4) GPa^?1] and K′(b) = 2.6(3) for the b-axis; K(c) = 132(4) GPa [β _c = 0.00252(7) GPa^?1] and K′(c) = 3.3(3) for the c-axis. The elastic anisotropy of topaz at room-P can be expressed as: K(a):K(b):K(c) = 1.10:1.67:1.00 (β _a:β _b:β _c = 1.50:1.00:1.66). A series of structure refinements have been performed based on the intensity data collected at high pressure, showing that the P-induced structure evolution at the atomic scale is mainly represented by polyhedral compression along with inter-polyhedral tilting. A comparative analysis of the elastic behavior and P/T-stability of topaz polymorphs and “phase egg” (i.e., AlSiO₃OH) is carried out.     

High-pressure crystal chemistry of chrysoberyl,Al2BeO4: Insights on the origin of olivine elastic anisotropy

High-pressure crystal structure refinements and axial compressibilities have been determined by x-ray methods for the olivine isomorph chrysoberyl, Al₂BeO₄. Unlike silicate olivines, which are more than twice as compressible along b than along a, chrysoberyl (space group Pbnm) has nearly isotropic compressibility with β _a =1.12±0.04, β _b =1.46±0.05, and β _c =1.31±0.03 (all×10^?4 kbar^?1). The resultant bulk modulus is 2.42±0.05 Mbar, with K′ assumed to be 4. The axial compression ratios of chrysoberyl are 1.00:1.30:1.17, compared to axial compression ratios 1.00:2.02:1.60 for forsterite. These differences in compression anisotropy arise from differences in relative bond compressibilities. In chrysoberyl the average aluminum-oxygen and beryllium-oxygen bond compressibilities are similar, yielding nearly isotropic compression, but in silicate olivines octahedral cation-oxygen bonds are significantly more compressible than Si-O bonds, so that compression parallel to a is much more restricted than that parallel to b. The inherent anisotropy of the olivine structure is not, by itself, sufficient to cause anisotropic compression. It appears that in the case of olivine the distribution of cations of different valences, in conjunction with the structure type, leads to anisotropies in physical properties.     

Xitieshanite—A new ferric sulphate mineral

Xitieshanite is a new ferric sulfate mineral discovered in the oxidation zone of a Pb-Zn deposit at Xitieshan, Qinghai Province, China. The typical crystal of xitieshanite is a rhombic rectangle. It is bright green in colour with a light yellow tint. Luster vitrous Translucent to almost transparent. Streak yellow. Cleavage imperfect. Fracture uneven or conchoidal. H. (Vickers)=62.6kg/mm². Specific gravity=1.99_obs(2.02_calc,) Pleochroism strong, and axial colours: X=colourless to pale yellow, Y=pale yellow, Z=light yellow with greenish tint. It is optically positive, biaxial, 2V=77°,r v. Refractive indices:N _x =1.536,N _y =1.570,N _z =1.628. Extinction parallel and inclined. Elongation positive and negative. X-ray single-crystal study shows it is monoclinic. Space groupP2₁/a. Unit cell parameters:a=14.102,b=6.908,c=10.673 Å, β=111.266°,V=968.9, ų,Z=4. The powder pattern of xitieshanite gave the strongest lines: 6.67(6)(201), 6.09(5)(110), 5.69(5)(011), 4.96(10)(002), 4.81(10)(211), 4.21(5)(112), and 3.90(9)(211). Chemical analysis gave Al₂O₃ 0.01, Fe₂O₃ 26.15, FeO 0.18, MgO 0.03, CaO 0.09, K₂O 0.03, Na₂O 0.07, SO₃ 27.69, H₂O 45.02, total 99.27%, corresponding to the chemical formula: Fe²⁺ (SO₄)(OH) · 7H₂O. The DTA curve shows respectively three strong endothermic peaks at 85°, 170°, and 735°C, and a weak peak at 460°C. The TGA curve shows a loss of weight in three different steps. The infrared spectral curve of xitieshanite demonstrates that it has two principal absorption bands at 3,350 and 1,225–1,003 cm^?1 and two subordinate bands at 1,620 and 603 cm^?1.     

Vladimirivanovite, Na6Ca2[Al6Si6O24](SO4,S3,S2,Cl)2 · H2O, a new mineral of sodalite group

The results of an examination of vladimirivanovite, a new mineral of the sodalite group, found at the Tultui deposit in the Baikal region are discussed. The mineral occurs in the form of outer rims (0.01–3 mm thick) of lazurite, elongated segregations without faced crystals (0.2 to 3–4 mm in size; less frequently, 4 × 12–15 × 20 mm), and rare veinlets (up to 5 mm) hosted in calciphyre and marble. Vladimirivanovite is irregular and patchy dark blue. The mineral is brittle; on average, the microhardness VHN is 522–604, 575 kg/mm²; and the Mohs hardness is 5.0–5.5. The measured and calculated densities are 2.48(3) and 2.436 g/cm³, respectively. Vladimirivanovite is optically biaxial; 2V _meas = 63(±1)°, 2V _calc = 66.2°; the refractive indices are α = 1.502–1.507 (±0.002), N _m = 1.509–1.514 (±0.002), and N _g = 1.512–1.517 (±0.002). The chemical composition is as follows, wt %: 32.59 SiO₂, 27.39 Al₂O₃, 7.66 CaO, 17.74 Na₂O, 11.37 SO₃, 1.94 S, 0.12 Cl, and 1.0 H₂O; total is 99.62. The empirical formula calculated based on (Si + Al) = 12 with sulfide sulfur determined from the charge balance is Na_6.36Ca_1.52(Si_6.03Al_5.97)_Σ12O_23.99(SO₄)_1.58(S₃)_0.17(S₂)_0.08 · Cl_0.04 · 0.62H₂O; the idealized formula is Na₆Ca₂[Al₆Si₆O₂₄](SO₄,S₃,S₂,Cl)₂ · H₂O. The new mineral is orthorhombic, space group Pnaa; the unit-cell dimensions are a = 9.066, b = 12.851, c = 38.558 Å, V = 4492 ų, and Z = 6. The strongest reflections in the X-ray powder diffraction pattern (dÅ—I[hkl]) are: 6.61–5[015], 6.43–11[020, 006], 3.71–100[119, 133], 2.623–30[20.12, 240], 2.273–6[04.12], 2.141–14[159, 13.15], 1.783–9[06.12, 04.18], and 1.606–6[080, 00.24]. The crystal structure has been solved with a single crystal. The mineral was named in memoriam of Vladimir Georgievich Ivanov (1947–2002), Russian mineralogist and geochemist. The type material of the mineral is deposited at the Mineralogical Museum of St. Petersburg State University, St. Petersburg, Russia.     

Natrolite,part I: Refinement of high-order data,separation of internal and external vibrational amplitudes from displacement parameters

A single crystal of natrolite, Na₂Al₂Si₃O₁₀·2H₂O, was studied by X-ray diffraction methods at room temperature. The intensities were measured with MoKα radiation (λ = 0.7107 Å) in a complete sphere of reflection up to sin θ/λ = 0.903 Å^?1. The structure was refined in the orthorhombic space group Fdd2 with a = 18.2929 (7) Å, b = 18.6407(9) Å, c = 6.5871(6) Å, V = 2246 ų, Z = 8. A refinement of high-order diffraction data yielded reliability factors of R(F) = 0.9%, R _w(F) = 0.8%, GoF = 1.40 for 1856 high-angle reflections (0.7 ?in θ/λ <0.903 Å^?1) and R(F) = 1.0%, R _W(F) = 1.2%, GoF = 3.07 for all 3471 independent reflections in the complete sphere of reflection. The T-O distances as well as the T-O-T angles were found to be strongly influenced by the different bond strengths received by the individual oxygen atoms. The T O distances calculated using Baur's extended valence rule agree on average within 0.003 Å with the observed values. An analysis of the mean square displacement amplitudes allowed a separation of the external and internal vibrational amplitudes along the T-O bonds as well as along the Na O and H₂O-O bond directions and the calculation of force constants. The internal vibrational amplitudes (ΔU) of the T-O vibrations are in the range of 5 to 11 × 10^-4 Ų, that is about one order of magnitude smaller than the mean square displacement amplitudes of the external vibrations. The corresponding force constants are F = 354 to 824 Nm^?1. The values of the force constants of the motion of the Na-ion and the water molecule against the framework oxygen atoms lie in the range between F = 57 and 293 Nm^?1. This is the first instance where displacement amplitudes from a zeolite structure refinement could be apportioned between contributions from internal and external vibrations for individual bonds.     

High-pressure elastic behavior of Ca4La6(SiO4)6(OH)2 a synthetic rare-earth silicate apatite: a powder X-ray diffraction study up to 9.33 GPa

The compression behavior of a synthetic Ca₄La₆(SiO₄)₆(OH)₂ has been investigated to about 9.33 GPa at 300 K using in situ angle-dispersive X-ray diffraction and a diamond anvil cell. No phase transition has been observed within the pressure range investigated. The values of zero-pressure volume V ₀, K ₀, and $K_{0}^{'}$ refined with a third-order Birch–Murnaghan equation of state are V ₀ = 579.2 ± 0.1 Å³, K ₀ = 89 ± 2 GPa, and $K_{0}^{'} = 10.9 \pm 0.8$ . If $K_{0}^{'}$ is fixed at 4, K ₀ is obtained as 110 ± 2 GPa. Analysis of axial compressible modulus shows that the a-axis (K _a0 = 79 ± 2 GPa) is more compressible than the c-axis (K _c0 = 121 ± 7 GPa). A comparison between the high-pressure elastic response of Ca₄La₆(SiO₄)₆(OH)₂ and the iso-structural calcium apatites is made. The possible reasons of the different elastic behavior between Ca₄La₆(SiO₄)₆(OH)₂ and calcium apatites are discussed.     

Stability at high-pressure,elastic behaviour and pressure-induced structural evolution of CsAlSi<Subscript>5</Subscript>O<Subscript>12</Subscript>, a potential host for nuclear waste

The elastic and structural behaviour of the synthetic zeolite CsAlSi₅O₁₂ (a = 16.753(4), b = 13.797(3) and c = 5.0235(17) Å, space group Ama2, Z = 2) were investigated up to 8.5 GPa by in situ single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions. No phase-transition occurs within the P-range investigated. Fitting the volume data with a third-order Birch–Murnaghan equation-of-state gives: V ₀ = 1,155(4) ų, K _T0 = 20(1) GPa and K′ = 6.5(7). The “axial moduli” were calculated with a third-order “linearized” BM-EoS, substituting the cube of the individual lattice parameter (a ³, b ³, c ³) for the volume. The refined axial-EoS parameters are: a ₀ = 16.701(44) Å, K _T0a = 14(2) GPa (β_a = 0.024(3) GPa^?1), K′ _a = 6.2(8) for the a-axis; b ₀ = 13.778(20) Å, K _T0b = 21(3) GPa (β_b = 0.016(2) GPa^?1), K′ _b = 10(2) for the b-axis; c ₀ = 5.018(7) Å, K _T0c = 33(3) GPa (β_c = 0.010(1) GPa^?1), K′ _c = 3.2(8) for the c-axis (K _T0a:K _T0b:K _T0c = 1:1.50:2.36). The HP-crystal structure evolution was studied on the basis of several structural refinements at different pressures: 0.0001 GPa (with crystal in DAC without any pressure medium), 1.58(3), 1.75(4), 1.94(6), 3.25(4), 4.69(5), 7.36(6), 8.45(5) and 0.0001 GPa (after decompression). The main deformation mechanisms at high-pressure are basically driven by tetrahedral tilting, the tetrahedra behaving as rigid-units. A change in the compressional mechanisms was observed at P ≤ 2 GPa. The P-induced structural rearrangement up to 8.5 GPa is completely reversible. The high thermo-elastic stability of CsAlSi₅O_12, the immobility of Cs at HT/HP-conditions, the preservation of crystallinity at least up to 8.5 GPa and 1,000°C in elastic regime and the extremely low leaching rate of Cs from CsAlSi₅O₁₂ allow to consider this open-framework silicate as functional material potentially usable for fixation and deposition of Cs radioisotopes.     

Aqueous oxidation of trichloroethene (TCE): a kinetic analysis

An empirical kinetic rate law appropriate for many ground waters (neutral pH, aerobic) has been determined for the aqueous oxidation of trichloroethene (TCE), one of the most volumetrically important chlorinated hydrocarbon pollutants. Mass balances were monitored by measuring both the rate of disappearance of TCE and the rate of appearance of CO₂ and Cl⁻. Dilute buffer solutions were used to fix pH and stoichiometrically sufficient amounts of dissolved O₂ were used to make the reactions pseudo zero-order in O₂. Using a standard chemical kinetic approach, two orders-of-magnitude in initial TCE concentration were spanned and the resulting double-log plot (log concentration vs. log initial rate) was used to determine the rate constant (k=5.77±1.06×10⁻⁷ s⁻¹) and “true” (i.e., with respect to concentration, not time) reaction order (n_c=0.85±0.03) for the rate law. By determining rate constants over the temperature interval 343–373 K, the Arrhenius activation energy (E_a) for the reaction was determined to be 108.0±4.5 kJ/mol. The rate law and derived kinetic parameters may be used in reactive transport simulators in order to account for aqueous oxidation of TCE as a function of temperature.