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1.
The equilibrium $${\text{(1}} - y{\text{)Fe}}_{(s)} + \tfrac{{\text{1}}}{{\text{2}}}{\text{O}}_{{\text{2(g)}}} \rightleftarrows {\text{Fe}}_{{\text{1}} - y} {\text{O}}_{{\text{(}}s,{\text{ in MW)}}} $$ was studied by measuring oxygen potentials for a range of different magnesiowüstite compositions relative to those of the iron-wüstite system in an oxygen concentration cell involving yttria stabilized zirconia as the solid electrolyte. The temperature range covered was 1050 to 1400 K. Separate measurements of the mole fraction of trivalent iron in magnesiowüstite (x(Fe3+)) were made and the composition dependence ofx(Fe3+) was taken into account in calculations of the activity-composition relations of FeO, Fe2/3O and MgO.  相似文献   

2.
Given the direction cosines a i ′ = (a 1 i , a 2 i , a 3 i )corresponding to a set of pspherically projected fabric poles, an initial estimate x′ = (x1, x2, x3, x4)for the angular radius x4,and direction cosines of the center of the least-squares small circle which minimizes the sum of the squares of the angular residuals $$r = \sum\limits_p {\left[ {x_4 - \cos ^{ - 1} \left( {a_1^i x_1 + a_2^i x_2 + a_3^i x_3 } \right)} \right]} ^2 $$ can be iteratively improved by taking xj+1 = xj + Δxwhere xj is the value of xat the jth iteration and $$\Delta x = - H_j^{ - 1} \left[ {q_j + x_j \left( {x'_j H_j^{ - 1} x_j } \right)\left( {q_j - x'_j H_j^{ - 1} q_j } \right)} \right],$$ where As an initial approximation for xwe have found it convenient to ignore the fact that the data are constrained to lie on the surface of the reference sphere and to use the parameters of a least-squares plane through the given poles. Generalization of this approach to fitting variously constrained great and small circles is easily made. The relative merits of differently constrained fits to the same data can be tested approximately if it is assumed that the errors in the location of the poles are isotropic and normally distributed. It is thus possible to statistically assess the relative significance of conflicting structural models which predict different geometrical patterns of fabric elements.  相似文献   

3.
Suppose that ¯(x1),...,¯Z(xn). are observations of vector-valued random function ¯(x). In the isotropic situation, the sample variogram γ*(h) for a given lag h is $$\bar \gamma ^ * (h) = \frac{1}{{2N(h)}}\mathop \sum \limits_{s(h)} (\overline Z (x_1 ) - \overline Z (x_1 )) \overline {(Z} (x_1 ) - \overline Z (x_1 ))^T $$ where s(h) is a set of paired points with distance h and N(h) is the number of pairs in s(h).. For a selection of lags h1, h2, .... hk such that N (h1) > O. we obtain a ktuple of (semi) positive definite matrices $\bar \gamma ^ * (h_{ 1} ),. . . ., \bar \gamma ^ * (h_{ k} )$ . We want to determine an orthonormal matrix B which simultaneously diagonalizes the $\bar \gamma ^ * (h_{ 1} ),. . . ., \bar \gamma ^ * (h_{ k} )$ or nearly diagonalizes them in the sense that the sum of squares of offdiagonal elements is small compared to the sum of squares of diagonal elements. If such a B exists, we linearly transform $\overline Z (x)$ by $\overline Y (x) = B\overline Z (x)$ . Then, the resulting vector function $\overline Y (x)$ has less spatial correlation among its components than $\overline Z (x)$ does. The components of $\overline Y (x)$ with little contribution to the variogram structure may be dropped, and small crossvariograms fitted by straightlines. Variogram models obtained by this scheme preserve the negative definiteness property of variograms (in the matrix-valued function sense). A simplified analysis and computation in cokriging can be carried out. The principles of this scheme arc presented in this paper.  相似文献   

4.
The variance-based cross-variogram between two spatial processes, Z1 (·) and Z2 (·), is var (Z1 ( u ) – Z2 ( v )), expressed generally as a bivariate function of spatial locations uandv. It characterizes the cross-spatial dependence between Z1 (·) and Z2 (·) and can be used to obtain optimal multivariable predictors (cokriging). It has also been called the pseudo cross-variogram; here we compare its properties to that of the traditional (covariance-based) cross-variogram, cov (Z1 ( u ) – Z1 ( v ), Z2 ( u ) – Z2 ( v )). One concern with the variance-based cross-variogram has been that Z1 (·) and Z2 (·) might be measured in different units (apples and oranges). In this note, we show that the cokriging predictor based on variance-based cross-variograms can handle any units used for Z1 (·) and Z2 (·); recommendations are given for an appropriate choice of units. We review the differences between the variance-based cross-variogram and the covariance-based cross-variogram and conclude that the former is more appropriate for cokriging. In practice, one often assumes that variograms and cross-variograms are functions of uandv only through the difference u – v. This restricts the types of models that might be fitted to measures of cross-spatial dependence.  相似文献   

5.
In the course of a thorough study of the influences of the second coordination sphere on the crystal field parameters of the 3d N -ions and the character of 3d N –O bonds in oxygen based minerals, 19 natural Cr3+-bearing (Mg,Ca)-garnets from upper mantle rocks were analysed and studied by electronic absorption spectroscopy, EAS. The garnets had compositions with populations of the [8] X-sites by 0.881 ± 0.053 (Ca + Mg) and changing Ca-fractions in the range 0.020 ≤ w Ca[8] ≤ 0.745, while the [6] Y-site fraction was constant with x Cr3+ [6] = 0.335 ± 0.023. The garnets had colours from deeply violet-red for low Ca-contents (up to x Ca = 0.28), grey with 0.28 ≤ x Ca ≤ 0.4 and green with 0.4 ≤ x Ca. The crystal field parameter of octahedral Cr3+ 10Dq decreases strongly on increasing Ca-fraction from 17,850 cm−1 at x Ca[8] = 0.020 to 16,580 cm−1 at x Ca[8] = 0.745. The data could be fit with two model which do statistically not differ: (1) two linear functions with a discontinuity close to x Ca[8] ≈ 0.3,
(2) one continuous second order function,
The behaviour of the crystal field parameter 10Dq and band widths on changing Ca-contents favour the first model, which is interpreted tentatively by different influences of Ca in the structure above and below x Ca[8] ≈ 0.3. The covalency of the Cr–O bond as reflected in the behaviour of the nephelauxetic ratio decreases on increasing Ca-contents.  相似文献   

6.
Zusammenfassung Der Hügelit, das Arsenat-Analogon zum Dumontit, gehört zu den Sekundärmineralien der Grube Michael im Weiler bei Lahr im Schwarzwald (Bundesrepublik Deutschland), wo er zusammen mit Hallimondit, Widenmannit, Mimetesit, Cerussit und Zeunerit in Drusen von hornsteinartigem Quarz auftritt. Beobachtete kristallographische Formen: {100}, {110}, {001}, {011} sowie (?) {010}.Spaltbarkeit nach {100} sehr gut, nach {110} unsicher. Bruch muschelig. Härte etwa 2 1/2; spröde.Farbe braun bis orangegelb; durchsichtig bis durchscheinend. Strich hellgelb. Keine UV-Fluoreszens. Brechungsindizes:n =1,898(5),n =1,915(5), 2V =25° (für =592 nm); sehr starke Achsenwinkeldispersion.Gitterkonstanten:a 0=8,13,b 0=17,27,c 0=7,01 Å, =109°. Raumgruppe:P21/m oderP21.D x=5,80 g·cm–3 (mit der Formel Pb2(UO3)3(AsO4)2(OH)4·3H2O undZ=2). Stärkste Linien des Pulverdiagramms: 3,73(10), 3,06(9), 3,00(7) und 2,89(7).
On Hügelite
Summary Hügelite, the arsenate analogue of dumontite, occurs amongst the secondary minerals of the Michael Mine at Weiler near Lahr in the Black Forest (German Federal Republic), in vugs of dense quartz in association with hallimondite, widenmannite, mimetite, cerussite and zeunerite. Observed crystal forms: {100}, {110}, {001}, {011} and (?) {010}.Cleavage: {100} very good, {110} uncertain. Fracture conchoidal. Hardness about 2 1/2, brittle.Colour brown to orange yellow, transparent to translucent. Not fluorescent in ultraviolet light. Indices of refraction:n =1.898(5),n =1.915(5); 2V =25° (for =592 nm); strong dispersion of the axial angle.Unit-cell dimensions:a 0=8.13,b 0=17.27,c 0=7.01 Å, =109°, space groupP21/m orP21.D x=5.80 g·cm–3 (with the formula Pb2(UO2)3(AsO4)2(OH)4·3H2O andZ=2). Strongest lines of the powder pattern: 3.73(10); 3.06(9); 3.00(7); 2.89(7).

Mit 2 Abbildungen

Herrn Univ. Prof. Dr.H. Meixner zum 70. Geburtstag gewidmet.  相似文献   

7.
The thermodynamic stability constants for the hydrolysis and formation of mercury (Hg2+) chloride complexes
have been used to calculate the activity coefficients for Hg(OH) n (2–n)+ and HgCl n (2–n)+ complexes using the Pitzer specific interaction model. These values have been used to determine the Pitzer parameters for the hydroxide and chloro complexes and C ML). The values of and have been determined for the neutral complexes (Hg(OH)2 and HgCl2). The resultant parameters yield calculated values for the measured values of log to  ±0.01 from I  =  0.1 to 3 m at 25°C. Since the activity coefficients of and are in reasonable agreement with the values for Pb(II), we have estimated the effect of temperature on the chloride constants for Hg(II) from 0 to 300°C and I = 0–6 m using the Pitzer parameters for complexes. The resulting parameters can be used to examine the speciation of Hg(II) with Cl− in natural waters over a wide range of conditions.  相似文献   

8.
Summary The crystal structure of a schröckingerite from Joachimsthal, NaCa3[UO2(CO3)3](SO4) F·10H2O, triclinic, space groupP1,a=9.634(1),b=9.635(1),c=14.391(2) Å, -91.41(1), =92.33(1), =120.26(1)°,V=1151 Å3,Z=2, has been determined by X-ray diffraction and refined toR=0.026 for 5451 reflections. The structure contains NaCa3[UO2(CO3)3] (SO4) F·6H2O layers built up from UO2(CO3) 3 4– anions, NaO3(H2O)3 octahedra, three kinds of CaO5F(H2O)2 polyhedra, Ca3F pyramids and Ca-bonded SO4 tetrahedra. These layers extend atz1/5 andz4/5 parallel to (001). They are linked parallel to c exclusively by hydrogen bonds, both directly as well as via interlayer H2O molecules. The structure shows a striking trigonal pseudosymmetry within the range 0.04<z<0.96. Atz0 these parts of the structure are dislocated relative to each other by a step of 1 Å parallel to [110]. Morphologic and optical properties of schröckingerite have been investigated in the light of the known crystal structure.
Kristallstruktur und kristallographische Eigenschaften eines Schröckingerits von Joachimsthal
Zusammenfassung Die Kristallstruktur eines Schröckingerits von Joachimsthal, NaCa3[UO2(CO3)3](SO4) F·10H2O, triklin, RaumgruppeP1,a=9,634(1),b=9,635(1),c=14,391(2) Å, =91,41(1), =92,33(1), =120,26(1)°,V=1151 Å3,Z=2, wurde mit Röntgenbeugung bestimmt und für 5451 Reflexe aufR=0.026 verfeinert. Die Kristallstruktur enthält NaCa3[UO2(CO3)3] (SO4)I·6H2O Schichten, die aus UO2(CO3) 3 4– . Anionen, NaO3(H2O)3-Oktaedern, drei Arten von CaO5F(H2O)2-Polyedern, Ca3 F-Pyramiden und an Ca gebundenen SO4-Tetraedern aufgebaut sind. Diese Schichten erstrecken sich inz1/5 undz4/5 parallel zu (001). Sie sind parallel zuc ausschließlich durch Wasserstoffbrücken verknüpft, und zwar sowohl direkt als auch indirekt durch zwischen den Schichten gelegene Wassermoleküle. Die Struktur zeigt im Bereich 0,04<z<0,96 eine ausgeprägte trigonale Pseudosymmetrie. Derartige Bereiche sind inz0 um etwa 1 Å parallel zu [110] stufenartig gegeneinander versetzt. Morphologische und optische Eigenschaften von Schröckingerit wurden im Licht der bekannten Kristallstruktur untersucht.

With 6 Figures  相似文献   

9.
Summary Phosphates of compositions (Na1–xLix)1.5Mn1.5Fe1.5(PO4)3 were synthesized by solid state reactions in air, and pure alluaudite-type compounds were obtained for x=0.00, 0.25, and 0.50. Rietveld refinements of X-ray powder diffraction data indicate the occurrence of Mn2+ in the M(1) site, and of Fe3+ and Mn2+ in the M(2) site. For x=0.25 and 0.50, A(1) is occupied by Li+ and Na+, whereas A(2) is occupied by Na+ and vacancies. A careful examination of the number of electrons occurring in the A sites of the alluaudite-type compounds (Na1–xLix)MnFe2(PO4)3 and (Na1–xLix) CdIn2(PO4)3 confirms that lithium occupies only the A(1) crystallographic site of the alluaudite structure.  相似文献   

10.
Summary Thermochemistry, morphology, optical properties and crystal structure of synthetic bayleyite, Mg2[UO2(CO3)3]·18H2O, monoclinic, have been studied. Incongruent melting at 55°, three steps of dehydration and two steps of decarboxylation have been found by thermochemic investigations. Morphology: Prisms along [001] with {100}, {110}, {210}, {001}, {401}, {021}, {211}, {111} and as the most important forms. Optical data:n =1.453,n =1.498,n =1.499, 2V x =16°,Y=b,X c=11°. Crystal structure: Space groupP21/a,a=26.560(3),b=15.256(2),c=6.505(1) Å, =92.90(1)°,Z=4,R=0.029 for 5126 independent reflections measured with MoK -radiation. The structure is built up from isolated Mg(H2O)6 octahedra, UO2(CO3)3 units and lattice water molecules, all held together by hydrogen bonds only.
Synthetischer Bayleyit, Mg2[UO2(CO3)3]·18H2O: Thermochemie, Kristallographie und Kristallstruktur
Zuseammenfasung Thermochemie, Morphologie, optische Eigenschaften und Kristallstruktur von Bayleyit, Mg2[UO2(CO3)3]·18H2O, monoklin, wurden anhand künstlich hergestellter Kristalle untersucht. Durch thermochemische Untersuchung wurden inkongruentes Schmelzen bei 55°, eine dreistufige Wasserabgabe sowie eine zweistufige CO2-Abgabe festgestellt. Morphologie: parallel zu [001] gestreckte Prismen mit {100}, {110}, {210}, {001}, {401}, {021}, {211}, {111}, und {311} als wichtigste Formen. Optische Daten:n =1.453,n =1.498,n =1.499, 2V x =16°,Y=b,X c=11°. Kristallstruktur: RaumgruppeP21/a,a=26.560(3),b=15.256(2),c=6.505(1) Å, =92.90(1)°,Z=4;R=0.029 für 5126 unabhängige, mit MoK -Strahlung gemessene Reflexe. Die Struktur enthält isolierte Mg(H2O)6-Oktaeder, UO2(CO3)3-Gruppen und freie Wassermoleküle, die ausschließlich durch Wasserstoffbrücken miteinander verknüpft sind.

With 4 Figures  相似文献   

11.
Zusammenfassung Die Phase Cu2FeSnSe3,8 ist tetragonal, Raumgruppe mit 0=5.69 undc 0=11,26 Å.Z=2,D x=5,441. Synthesetemperatur: 410°C.
The compound Cu2FeSnSe3,8 in comparison to stannite
Summary The phase Cu2FeSnSe3,8 is tetragonal, space-group with 0=5.69 andc 0=11.26 Å.Z=2,D x=5.441. Temperature of synthesis: 410°C.
  相似文献   

12.
Single crystal Raman spectra of pyrite-type RuS2, RuSe2, OsS2, OsSe2, PtP2, and PtAs2 are presented and discussed with reference to the energies of the X-X stretching modes x-x (A g, F g) and the X2 librations (E, 2Fg). The main results obtained are (i) strong Raman resonance effects, (ii) different sequences for x-x (A g) and (E g), i.e., R_{x_2 } $$ " align="middle" border="0"> for PtP2 and PtAs2 and R_{x_2 } $$ " align="middle" border="0"> for OsS2, owing to the interplay of intraionic and interionic lattice forces, (iii) greater strengths for the intraionic P-P and As-As bonds compared to the S-S and Se-Se bonds, respectively, and (iv) a strong influegnce of the metal ions on the strength of the X-X bonds.This is contribution LXI of a series of papers on lattice vibration spectra  相似文献   

13.
Britvinite, a new mineral species, has been found in manganese ore at the Långban deposit, Bergslagen ore district, Filipstad, Värmland County, Sweden. Calcite, barytocalcite, brucite, cerussite, and hausmannite are associated minerals. Britvinite occurs as pale yellow to colorless transparent plates with a white streak up to 0.2 × 0.5 × 0.5 mm in size, which are flat parallel to {001}; the luster is adamantine. Thin lamellae are flexible, whereas thick ones are brittle; the Mohs hardness is 3. The cleavage is eminent parallel to {001}. The calculated density is 5.51 g/cm3. In the infrared spectrum of the new mineral, the bands of (OH)?, (CO3)2?, and (BO3)3? are recorded, whereas those corresponding to water molecules are absent. Britvinite is optically biaxial and negative, α = 1.896(2), β = 1.903(2), γ = 1.903(2), 2Vmeas = 20(10), Z≈c. Dispersion is strong, r<v. The chemical composition (electron microprobe; H2O determined with the Alimarin method, CO2, with selective sorption) is (wt %) 7.95 MgO, 71.92 PbO, 0.41 Al2O3, 12.77 SiO2, 2.2 H2O, 2.1 CO2, 2.67 B2O3 (calculated on the basis of structural data); total 100.02. The empirical formula calculated on the basis of 59 anions (O + OH) (Z = 1) is as follows: Pb14.75Mg9.03Si9.73Al0.37O30.76(BO3)3.51(CO3)2.18(OH)11.7. The simplified formula (Z = 2) is Pb7 + x Mg4.5(Si5O14)(BO3)2(CO3)(OH,O)7 (x < 0.5). The crystal structure of britvinite has been studied on a single crystal at 173 K; R = 0.0547. The new mineral is triclinic, space group P $ \bar 1 Britvinite, a new mineral species, has been found in manganese ore at the L?ngban deposit, Bergslagen ore district, Filipstad, V?rmland County, Sweden. Calcite, barytocalcite, brucite, cerussite, and hausmannite are associated minerals. Britvinite occurs as pale yellow to colorless transparent plates with a white streak up to 0.2 × 0.5 × 0.5 mm in size, which are flat parallel to {001}; the luster is adamantine. Thin lamellae are flexible, whereas thick ones are brittle; the Mohs hardness is 3. The cleavage is eminent parallel to {001}. The calculated density is 5.51 g/cm3. In the infrared spectrum of the new mineral, the bands of (OH)−, (CO3)2−, and (BO3)3− are recorded, whereas those corresponding to water molecules are absent. Britvinite is optically biaxial and negative, α = 1.896(2), β = 1.903(2), γ = 1.903(2), 2Vmeas = 20(10), Z≈c. Dispersion is strong, r<v. The chemical composition (electron microprobe; H2O determined with the Alimarin method, CO2, with selective sorption) is (wt %) 7.95 MgO, 71.92 PbO, 0.41 Al2O3, 12.77 SiO2, 2.2 H2O, 2.1 CO2, 2.67 B2O3 (calculated on the basis of structural data); total 100.02. The empirical formula calculated on the basis of 59 anions (O + OH) (Z = 1) is as follows: Pb14.75Mg9.03Si9.73Al0.37O30.76(BO3)3.51(CO3)2.18(OH)11.7. The simplified formula (Z = 2) is Pb7 + x Mg4.5(Si5O14)(BO3)2(CO3)(OH,O)7 (x < 0.5). The crystal structure of britvinite has been studied on a single crystal at 173 K; R = 0.0547. The new mineral is triclinic, space group P ; the unit-cell dimensions are a = 9.3409(8), b = 9.3597(7), c = 18.8333(14) ?, α = 80.365(6)°, β = 75.816(6)°, γ = 59.870(5)°, V = 1378.74(19) ?3. The structure consists of alternating TOT stacks (containing octahedral brucite-like and discontinuous tetrahedral (Si5O14)∞∞ layers) and multilayered [Pb7.1(OH)3.6(CO3)(BO3)1.75(SiO4)0.25]∞∞ blocks. The strongest reflections in the X-ray powder diffraction pattern [d, ? (I, %)(hkl)] are 18.1(100)(001), 3.39(30)(12, 14, 015), 3.02(90)(006, 130, 106, 20, 11), 2.698(70)(332, 134, 030, 1), 2.275(30)(008, 420, 424), 1.867(30)(446, 239, 2.1.10, 18), 1.766(40)(151, 31, 10, 453, 542, 512, 42), 1.519(40)(0.0.12). The mineral has been named in honor of Sergei Nikolaevich Britvin (b. 1965), a Russian mineralogist. The type material of britvinite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. The registration number is 3458/1. Original Russian Text ? N.V. Chukanov, O.V. Yakubovich, I.V. Pekov, D.I. Belakovsky, W. Massa, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, Pt CXXXVI, No. 6, pp. 18–25. The new mineral britvinite and its name were accepted by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society, June 7, 2006, and approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, October 17, 2006.  相似文献   

14.
Spatial prediction and ordinary kriging   总被引：11，自引：0，他引：11  
Suppose data {Z(s i ):i=1, ..., n} are observed at spatial locations {s i :i=1, ..., n}. From these data, an unknownZ(s 0) is to be predicted at a known locations 0c, or, ifZ(s0) has a component of measurement error, then a smooth versionS(s 0) should be predicted. This article considers the assumptions needed to carry out the spatial prediction using ordinary kriging, and looks at how nugget effect, range, and sill of the variogram affect the predictor. It is concluded that certain commonly held interpretations of these variogram parameters should be modified.This paper was presented at MGUS 87 Conference, Redwood City, California, 14 April 1987.  相似文献   

15.
Fluids at crustal pressures and temperatures   总被引：1，自引：0，他引：1  
  相似文献   

16.
Chudakova  E. M. 《Astronomy Reports》2019,63(5):353-364

A method for determining the thickness of the stellar disk of a galaxy from a photometric image of the galaxy in the plane of the sky is proposed and justified. The method can be applied to determine the thickness of plane-parallel exponential disks with an arbitrary, radius-independent, luminosity distribution perpendicular to the plane of the disk J(r, z) = exp(-r/h)f(z). A special feature and advantage of the method is that it enables determination of the thicknesses of disks viewed at arbitrary angles to the plane of the sky (but not strictly edge-on or face-on). The key idea of the method is finding the true inclinations of galaxies viewed at arbitrary angles not from their isophotes, but instead from the azimuthal distribution of the exponential parameter h. The difference between the inclination determined in the traditional way using the isophotes and the true inclination enables estimation of the thickness of the disk. The effectiveness of the method for determining the inclinations of plane-parallel disks is confirmed using a sample of model isothermal galactic disks: I(r, z) = I0 exp(-r/h)sech2(z/z0). The inclinations of the planes of the model galaxies to the line of sight and the relative thicknesses in the model sample vary arbitrarily, making it possible to determine the limits of applicability of the method: z0/h < 0.7 and 10° <i < 75°.A sample of 44 piecewise-exponential disks of galaxies of the southern sky clusters is used to illustrate the application of the technique to observational data. Comparing the distribution of inclinations calculated using the new method and the traditional isophote method shows that the new method yields a more uniform distribution of inclinations to the plane of the sky for the sample galaxies. The derived average disk thicknesses and the disk-thickness distributions are consistent with statistical estimates and observational data from the literature for samples of galaxies viewed edge-on

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17.
Zusammenfassung Röntgenographische Untersuchungen an Einkristallen von Arsenbrackebuschit, Pb2(Fe, Zn)(OH, OH2) (AsO4)2 (mit FeZn21), ergaben die RaumgruppeP21/m mita 0=7,763(1) Å,b 0=6.046(1) Å,c 0=9.022(1)Å, =112,5(1)°,V=391,2(1) Å3,Z=2 und x =6,54 g/cm3. Dreidimensionale Fouriersynthesen und Verfeinerungen nach der Methode der kleinsten Quadrate bis zu einemR-Wert von 0,073 zeigten, daß das neue Mineral strukturell einer Gruppe von Blei-Mineralen der allgemeinen Formel Pb2 Me(Z) (XO4) (YO4) — mitMe=Cu2+, Mn2+, Zn2+, Fe3+;X=S, Cr, V, As;Y=P, As, V;Z=OH, OH2 — zuzuordnen ist. Vertreter dieser Gruppe sind z. B. Tsumebit Pb2Cu(OH) (SO4) (PO4), Vauquelinit Pb2Cu(OH) (CrO4) (PO4) und auch Brackebuschit Pb2(Mn, Fe) (OH2) (VO4)2. Strukturelle Verwandtschaft besteht mit Tsumcorit Pb(Zn, Fe)2(OH, OH2)2(AsO4)2, einem weiteren Blei-Arsenat der gleichen Lagerstätte.
Structural investigation of arsenbrackebuschite
Summary X-ray single crystal work on arsenbrackebuschite, Pb2(Fe, Zn) (OH, OH2) (AsO4)2 (with FeZn21), gave space groupP21/m witha 0=7.763(1),b 0=6.046(1),c 0=9.022(1) Å, =112.5(1)°,V=391.2(1) Å3,Z=2 and x =6,54 g/cm3. 3-dimensional Fourier syntheses and least-squares refinement (finalR=0.073) showed that the new mineral belongs to a group of lead minerals with the general formula Pb2 Me(Z) (XO4) (YO4)Me=Cu2+, Mn2+, Zn2+, Fe2+, Fe3+;X=S, Cr, V, As; Y=P, As, V;Z=OH, OH2. Members of this group, are for example tsumebite, Pb2Cu(OH) (SO4)(PO4), vauquelinite, Pb2Cu(OH) (CrO4) (PO4), and brackebuschite, Pb2 (Mn, Fe) (OH2) (VO4)2. A structural relationship exists to tsumcorite, Pb(Zn, Fe)2(OH, OH2)2 (AsO4)2, another lead-arsenate from Tsumeb.

Mit 2 Abbildungen  相似文献   

18.
The local configurations around sodium ions in silicate glasses and melts and their distributions have strong implications for the dynamic and static properties of melts and thus may play important roles in magmatic processes. The quantification of distributions among charge-balancing cations, including Na+ in aluminosilicate glasses and melts, however, remains a difficult problem that is relevant to high-temperature geochemistry as well as glass science.Here, we explore the local environment around Na+ in charge-balanced aluminosilicate glasses (the NaAlO2-SiO2 join) and its distribution using 23Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy at varying magnetic fields of 9.4, 14.1, and 18.8 T, as well as triple-quantum (3Q)MAS NMR spectroscopy at 9.4 T, to achieve better understanding of the extent of disorder around this cation. We quantify the extent of this disorder in terms of changes in Na-O distance (d[Na-O]) distributions with composition and present a structural model favoring a somewhat ordered Na distribution, called a “perturbed” Na distribution model. The peak position in 23Na MAS spectra of aluminosilicate glasses moves toward lower frequencies with increasing Si/Al ratios, implying that the average d(Na-O) increases with increasing R. The peak width is significantly reduced at higher fields (14.1 and 18.8 T) because of the reduced effect of second-order quadrupolar interaction, and 23Na MAS NMR spectra thus provide relatively directly the Na chemical shift distribution and changes in atomic environment with composition. Chemical shift distributions obtained from 23Na 3Q MAS spectra are consistent with MAS NMR data, in which deshielding decreases with R. The average distances between Na and the three types of bridging oxygens (BOs) (Na-{Al-O-Al}, Na-{Si-O-Al}, and Na-{Si-O-Si}) were obtained from the correlation between d(Na-O) and isotropic chemical shift. The calculated d(Na-{Al-O-Al}) of 2.52 Å is shorter than the d(Na-{Si-O-Si}) of 2.81 Å, and d(Na-{Al-O-Al}) shows a much narrower distribution than the other types of BOs. 23Na chemical shifts in binary (Al-free) sodium silicate glasses are more deshielded and have ranges distinct from those of aluminosilicate glasses, implying that d(Na-NBO) (nonbridging oxygen) is shorter than d(Na-BO) and that d(Na-{Si-O-Si}) in binary silicates can be shorter than that in aluminosilicate glasses. The results given here demonstrate that high-field 23Na NMR is an effective probe of the Na+ environment, providing not only average structural information but also chemically and topologically distinct chemical shift ranges (distributions) and their variation with composition and their effects on static and dynamic properties.  相似文献   

19.
Summary Single crystal X-ray investigation shows that machatschkiite crystallizes in space groupR3c witha hex =15.127(2) Å andc hex =22.471(3) Å. The crystal structure was determined by direct methods and Fourier syntheses; the refinement by least squares methods led toR=0.04 for 645 independent reflections. Our X-ray results, supplemented by a partial electron microprobe analysis, indicate that the chemical formula of machatschkiite is close to Ca6–x Na x (AsO4)(AsO3OH)3(PO4)1–x (SO4) x ·15H2O (x0.3) withZ hex =6. The atomic arrangement of machatschkiite represents a new structure type and seems to be the first example of a crystal structure in which three oxygens of an AsO4 group are acceptors of each one hydrogen bond from three surrounding AsO3(OH) groups.
Machatschkiit: Kristallstruktur und Revision der chemischen Formel
Zusammenfassung Röntgenographische Einkristalluntersuchungen zeigten, daß Machatschkiit in der RaumgruppeR3c mita hex =15,127(2) Å undc hex =22,471(3) Å kristallisiert. Die Kristallstruktur wurde mit direkten Methoden und mit Fourier-Synthesen bestimmt; die Verfeinerung nach der Methode der kleinsten Quadrate führte für 645 Reflexe aufR=0.04. Unser Röntgenbefund, der durch eine partielle Elektronenstrahlmikroanalyse ergänzt wird, weist darauf hin, daß die chemische Formel des Machatschkiites mit guter Näherung Ca6–x Na x (AsO4)(AsO3OH)3 (PO4)1–x (SO4) x ·15H2O (x0,3) mitZ hex =6 lautet. Die Atomanordnung des Machatschkiites stellt einen neuen Strukturtyp dar und ist anscheinend das erste Beispiel, in welcher drei Sauerstoffe einer AsO4-Gruppe Akzeptoren von je einer Wasserstoffbindung dreier benachbarter AsO3OH-Gruppen sind.

With 4 Figures

Dedicated to the memory of Prof. Dr.F. Machatschki, Editor of Tschermaks Mineralogische und Petrographische Mitteilungen 1948–1968.  相似文献   

20.
Summary The crystal structure of curite, of which until now only the arrangement of the U and Pb atoms was known, has been redetermined with a synthetic crystal using three-dimensional X-ray techniques.R=0.043 for 1270 observed reflections. Curite is orthorhombic, space groupPnam-D 2h 16 ,a=12.513,b=13.002,c=8.373 ,Z=6.56 PbO·16UO3·9.44H2O. The structure consists of a novel type of washboard like puckered layers 2 [(UO2)8O8 (OH)6]6– formed by tetragonal bipyramidal [(UO2)O3(OH)] and pentagonal bipyramidal [(UO2)O3 (OH)2] polyhedra. The layers are parallel to {100} and are directly connected by hydrogen bonds. Lead atoms and oxygen atoms (H2O+OH) are located in folds between the layers, helping to connect them. The interlayer atomic positions are slightly disordered and one of them is partially occupied. The variable concentrations of the interlayer atoms are responsible for the changes in chemical composition.The structural formula [Pb8–x (OH)4–2x (H2O)2x ] [(UO2)8(OH)6]2 is suggested for curite;x=1.44 for the investigated synthetic curite. Within the three different U–O polyhedra the axial U–O distances are 1.81–1.88 , the equatorial 2.14–2.57 . The two different Pb atoms have ionic coordinations, each by ten oxygens with Pb–O distances of 2.46–3.32 , on the average 2.82 .
Die Kristallstruktur von Curit, [Pb 6,56 (H 2 O, OH) 4 ] [(UO 2)8 O 8(OH)6]2
Zusammenfassung Die Kristallstruktur von Curit, von der bisher nur die Lagen der Uran- und Bleiatome bekannt waren, wurde anhand eines künstlichen Kristalls mit dreidimensionalen Röntgendaten neu bearbeitet und für 1270 Reflexe aufR=0,043 verfeinert. Curit kristallisiert rhombisch, RaumgruppePnam-D 2h 16 ,a=12,513,b=13,002,c=8,373 ,Z=6,56 PbO·16 UO3·9,44 H2O. Die Struktur enthält gewellte Schichten eines neuen Typs, 2 [(UO2)8O8(OH)6]6–, die sich aus tetragonal bipyramidalen [(UO2)O3(OH)]- und pentagonal-bipyramidalen [(UO2)O3(OH)2]-Polyedern zusammensetzen. Die Schichten verlaufen parallel {100} und sind über Wasserstoffbrücken miteinander unmittelbar verknüpft. Zwischen den Schichten befinden sich Bleiatome und zusätzliche Sauerstoffatome (H2O+OH). Diese Atome weisen zum Teil Fehlordnung auf; eine der beiden Pb-Lagen ist nur partiell besetzt. Für Schwankungen in der chemischen Zusammensetzung von Curit ist der unterschiedliche Gehalt an Zwischenschichtatomen verantwortlich. Aufgrund dieser Untersuchung wird die Strukturformel [Pb8–x (OH)4–2x (H2O)2x ] [(UO2)8O8(OH)6]2 vorgeschlagen; für den untersuchten Curit istx=1,44. Die drei verschiedenen U–O-Polyeder der Struktur besitzen axiale bzw. äquatoriale U–O-Abstände von 1,81–1,88 bzw. 2,14–2,57 . Die zwei Arten von Bleiatomen besitzen eine ionische Koordination; beide sind von 10 Sauerstoffatomen in Abständen von 2,46–3,32 (Mittelwert 2,82 ) umgeben.

With 3 Figures  相似文献   

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