Palaeomagnetic data of late Cretaceous rocks from Sumba,Indonesia; the rotation of the Sumba continental fragment and its relation with eastern Sundaland

Sumba island forms part of a continental fragment, located near the transition of the Sunda Arc to the Banda Arc. It lies within the forearc region, between the active volcanic arc to the north and the Java Trench to the south. Palaeomagnetic studies of Cretaceous (late Albian-early Campanian) Lasipu sediments revealed a mean characteristic remanence (ChRM) direction with D = 42.5°, I = –23.0° and _{_95} = 6.1°, indicating a palaeolatitude of 12° S. This ChRM is, most likely, a secondary magnetization, possibly caused by the intrusion of the 65-Ma-old Tanadaro granodiorite. This granodiorite gave a mean ChRM direction with D = 44.7°, I = –16.3°, and ₉₅ = 12.2°, pointing to a palaeolatitude of 8.3° S. Eastern Sundaland with Borneo, west and south Sulawesi, and Sumba formed one continental unit in the late Mesozoic, most likely attached to the southeast Asian mainland. Borneo and west and south Sulawesi underwent large counterclockwise (CCW) rotations since the Jurassic with 45° during the Cretaceous, and 45° during the Palaeogene. The Sumba microcontinent, most likely, became detached from eastern Sundaland soon after deposition of the Lasipu sediments. Palaeomagnetic data show that Sumba underwent subsequent clockwise (CW) rotations of up to 96°: 53° between 82 and 65 Ma, and 38° between 65 and 37 Ma. Since the late Eocene, only small rotations occurred. The data indicate that eastern Sundaland, including Sumba, remained close to the equator since the Jurassic. CW rotations occurred in Sundaland both in the north (Indochina) and in the west (Sibumasu) as a consequence of the India – Eurasia collision. The same sense of rotation is seen further east in Sulawesis East Arm and the Philippine Sea plate. Eastern Sundaland (Borneo and west Sulawesi) with CCW rotations is being trapped between these CW rotating plates.     

Paleomagnetism of the Esterel rocks: a revisit 22 years after the thesis of Hans Zijderveld

For his PhD. thesis, Zijderveld (1975) studied the paleomagnetism of the Permian Esterel rocks (southern France). High-quality thermal and alternating-field demagnetization diagrams were interpreted to determine the direction of the characteristic natural magnetization. For the Esterel volcanics, a mean direction of Dec = 206.5°, Inc = –23°, ₉₅ = 5.7°, k = 112 was found for this magnetization. The dispersion in this mean is remarkably low. Only the declination of the Reyran Rhyolite in the Reyran River quarry clearly deviated from this mean. This deviating direction is not found in our samples, taken at the same site. As many faults occur in this quarry, it is suggested that Zijderveld sampled this rhyolite on a small rotated block. To verify whether the small dispersion in the mean paleomagnetic direction of the Esterel rocks has a geomagnetic or a rock-magnetic origin, two conglomerate tests were carried out. One of these might be interpreted as positive. The results of the other conglomerate test (Agay Formation) are ambiguous: four of the six measured boulders show directions close to the mean paleomagnetic direction of the Esterel rocks. Rock-magnetic measurements show that the remanence is carried by a magnetite and a hematite fraction. The low dispersion in the paleomagnetic directions, the conglomerate tests, and hematite as remanence carrier suggest that the characteristic remanence in the Esterel volcanics was not instantaneously acquired during cooling, but might be affected by remagnetization due to weathering.     

Palaeomagnetism of three dyke swarms in Nansen Land,north Greenland (83° N)

Three basic dyke swarms of post-Ellesmerian (post-Early Carboniferous) age in Nansen Land (83° N, 43° W) are still not dated numerically, but cross-cutting relationships show Group 1 to be older than Group 2, while Group 3 is the freshest and likely the youngest. Group 1 (the most northerly swarm) strikes N-S; Group 2 NW-SE, and Group 3 (the most southerly swarm) E-W. From more than 200 dykes 234 specimens from 28 sites were investigated palaeomagnetically. Group 1 dykes show unexpected shallow inclinations with a cleaned mean direction of (Dm, Im) = (151°, –5.8°), N = 7, k = 18.5, ₉₅ = 13.9°. They show hydrothermal alterations, some remagnetization by lightning, and the low inclination indicates a low palaeo latitude. The palaeopole is (Plat, Plon) = (8.9° S, 14.0° W) with (dp, dm) = (7°, 14°), and is close to the North American Early Carboniferous mean pole, suggesting a syn- or early late-tectonic dyke injection. The polarity is reverse. Groups 2 and 3 of presumed Cretaceous or Tertiary age show dominantly normal and reverse polarities, respectively. Their mean directions per polarity are well grouped, with (Dm, Im) = (–30.6°, 76.7°), n = 13, k = 191.4, ₉₅ = 3.9°, and (Dm, Im) = (133.4°, –76.7°), n = 10, k = 87.5, ₉₅ = 5.9°, respectively. They are antipodal within 95% significance, and combining both swarms gives (Dm, Im) = (–37.5°, 76.8°), n = 23, k = 124.3, ₉₅ = 2.7°, corresponding to a mean pole of (Plat, Plon) = (70.0° N, 185.1° E) with (dp, dm) = (4.7°, 5.0°), for which the spline of Late Cretaceous-Tertiary poles for all Greenland indicates a palaeomagnetic age of 57 ± 10 Ma. This pole (in present-day coordinates) is very close to the Late Cretaceous North American pole, in accordance with the fact that Greenland belongs to the North American craton, and that the two younger swarms are essentially postdating the opening of Baffin Bay.     

Admontit,ein neues Boratmineral aus der Gipslagerstätte Schildmauer bei Admont in der Steiermark (Österreich)

Zusammenfassung Admontit ist ein neues Magnesiumborat, das in der Gipslagerstätte Schildmauer bei Admont in der Steiermark (Österreich) in Vergesellschaftung mit drei weiteren neuen borhaltigen Mineralien sowie Gips, Anhydrit, Hexahydrit, Löweit, Quarz und Pyrit auftritt.Das Mineral bildet undeutlich ausgebildete farblose Kristalle von monokliner Symmetrie, die zum Teil nachc gestreckt und tafelig nach {100} sind. Keine Spaltbarkeit, Bruch muschelig, Härte wahrscheinlich 2–3,D _gem .=1,82,D _x =1,875g·cm^–3;n =1,442±0,002,n =1,504±0,002, 2V 30°,r. AE(010),n c auf (010) ca. 45°. a ₀=12,68,b ₀=10,07,c ₀=11,32 Å (alle Werte±0,02 Å),=109,68° (±0,1°),Z=2, RaumgruppeP2₁/c. Stärkste Linien des Pulverdiagramms: 12,08(9), 7,60(10), 3,93(8), 2,68(9). Formel: 2 MgO·6 B₂O₃·15 H₂O. In Wasser wird Admontit langsam zersetzt. Erhitzungsversuche zeigten, daß das Gitter zwischen 100 und 200°C zerstört wird. Ein Teil des Wassers entweicht schon unterhalb 100°C, der Rest zwischen 150 und 350°C.

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Admontite, a new borate mineral from the gypsum deposit Schildmauer near Admont in Styria (Austria)

Summary Admontite is a new magnesium borate found in the gypsum deposit of Schildmauer near Admont in Styria (Austria) in association with three other new borium-containing minerals and with gypsum, anhydrite, hexahydrite, löweite, quartz and pyrite.The mineral occurs in poorly developed colourless crystals of monoclinic symmetry, which in part are elongated along thec axis and flattened on {100}. No cleavage, fracture conchoidal, hardness probably 2–3,D _meas .=1.82,D _x =1.875g·cm^–3.n =1.442±0.002,n =1.504±0.002, 2V 30°,r. AE(010),n c on (010) about 45°.a ₀=12.68,b ₀=10.07,c ₀=11.32 Å (all±0.02 Å), =109.68° (±0.1°),Z=2,space groupP2₁/c. Strongest lines of the powder pattern: 12.08(9), 7.60(10), 3.93(8), 2.68(9). Chemical composition: 2 MgO·6 B₂O₃·15 H₂O. Admontite is slowly decomposed in water. Investigations of the thermal behaviour show that the lattice breaks down between 100 and 200°C. Part of the water escapes already under 100°C, the rest between 150 and 350°C.

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Mit 1 Abbildung

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Herrn Univ. Prof. Dr.H. Meixner zum 70. Geburtstag gewidmet.     

Crystal structure of KMn3+ [SeO4]2 — a triclinic distorted member of the Yavapaiite family

Summary The crystal structure of synthetic KMn[SeO₄]₂ was determined by single crystal X-ray diffraction methods in space group , a = 4.827(2) Å, b = 4.988(2) Å, c = 7.981(3) Å, = 83.18(1)°, = 85.32(2)°, = 67.92(1)°, V = 176.66 ų, Z = 1; 1564 unique data, measured up to 2 = 70° (MoK-radiation); R, R(I)_w = 0.034, 0.074.KMn[SeO₄]₂ is closely related to monoclinic yavapaiite, KFe[SO₄]₂, and isotypic compounds. Jahn-Teller distorted MnO₆ octahedra are alternately linked with KO₁₀ polyhedra along [001]. The mean values of the Mn-O and Se-O distances are 2.007 Å and 1.637 Å, respectively.

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Die Kristallstruktur vonKMn ³⁺[SeO₄]-einem triklin verzerrten Vertreter der Yavapaiite-Familie

Zusammenfassung Die Kristallstruktur von synthetisch dargestelltem KMn[SeO₄]₂ wurde mittels Einkristallröntgenmethoden in der Raumgruppe bestimmt: a = 4.827(2) Å, b = 4.988(2) Å, c = 7.981(3) Å, = 83.18(1)°, = 85.32(2)°, = 67.92(1)°, V = 176.66 ų, Z = 1; 1564 unabhängige Daten bis 2 = 70° (MoK-Strahlung); R, R(I)_w = 0.034, 0.074.KMn[SeO₄]₂ ist eng mit dem monoklinen Mineral Yavapaiit, KFe[SO₄]₂ und einer Reihe damit isotyper Verbindungen verwandt. Jahn-Teller verzerrte MnO₆ Oktaeder sind alternierend mit KO₁₀ Polyedern parallel [001] verbunden. Die Mittelwerte der Mn-O und Se-O Abstände sind 2.007 Å bzw. 1.637 Å.

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With 1 Figure     

1Tc-Strontiohilgardit (Ca,Sr)2[B5O8(OH)2Cl] und seine Stellung in der Hilgarditgruppe X2/II[B5O8(OH)2Cl]

Zusammenfassung 1Tc-Strontiohilgardit (Ca, Sr)₂ [B₅O₈(OH)₂,Cl] mit Ca : Sr etwa 1 : 1 ist ein neues Mineral der Hilgarditgruppe. Fundpunkt: Reyersbausen (9° 59,7 E, 51° 36,6 N), Grube Königshall-Hindenburg, Flöz Staßfurt in sylvinitischer Ausbildung.Konstanten : triklin-pedial,a ₀=6,38 Å,b ₀=6,480 Å,c ₀=6,608 Å, =75,4°,=61,2°, =60,5°; tafelige-gestreckte Links- und Re chtskristalle, farblos, wasserunlöslich, piezoelektrisch. Härte 5–7, Dichte 2,99 g cm^–3;n =1,638,n =1,639,n =1,670; 2V =19°.Neue Daten für die Hilgarditgruppe : 2 M (Cc)-Calciumhilgardit (=Hilgardit) =4 Ca₂[B₅O₃(OH)₂Cl], Raumgruppe Cc.3Tc-Calciumhilgardit (=Parahilgardit) = 3 Ca₂[B₅O₃(OH)₂Cl]; trinklin-pedial, ₀=6,31 Å,b =6,484 Å,c ₀=17,50 Å; =84,0°,=79,6°, =60,9°.Die Polymorphiebeziehungen sind geometrisch deutbar durch eine spezielle Art der Polytropie (Stapelung von Links- und Rechtskristallen im Elementarbereich).     

Comparison between two types of multifractal modeling

The interrelationships between two previously developed multifractal models are discussed. These are the Evertsz-Mandelbrot model developed on the basis of the multifractal spectrum f(), and the Schertzer-Lovejoy model based on the codimension function C() where and represent Hölder exponent and field order, respectively. It is shown how these two models are interrelated: they are identical for values of within the range D–(0)D–_min. where D is the Euclidean dimension. For D–_maxD–(0), however, f() remains a continuous function of whereas C() assumes constant value. In this respect, the fractal spectrum f() can provide more information about the multifractal measure than the codimension function C(). The properties of the two models are illustrated by application to the binomial multiplicative cascade model.     

Application of Gibbs Energy Minimization to ModelEarly-Diagenetic Solid-Solution Aqueous-Solution EquilibriaInvolving Authigenic Rhodochrosites in Anoxic BalticSea Sediments

The natural early-diagenetic environment ``anoxicporewater – authigenic mineral phases' has beencharacterized in sediment of the Gotland Deep,Baltic Sea, by a closed-system model. Occurrence ofcarbonate precipitates as thin almost pure whitelaminae was considered as a natural experiment forlong-term equilibration between these phases andporewater. Plots of distribution coefficientsindicate that metastable equilibrium exists betweenporewater and the authigenic Ca-rich rhodochrositephases below 7 cm depth. A thermodynamic model ofporewater geochemistry at in situ P = 25 barand T = 5 °C was developed using the Gibbsenergy minimization (GEM) approach. The values of isobaric-isothermal potentials of Mn, Ca, Fe, Mg,Sr, Ba, C, and O, calculated from the porewatercomposition, were used in a new ``dual thermodynamic'calculation approach to estimate solid activitycoefficients of the end-members in the non-idealsolid solution (Mn, Ca, Mg, Sr, Ba, Fe)CO₃,i.e., at full major and minor multi-componentcomplexity. The regular Margules interactionparameters for the composing binaries estimated bythis model were _Mn-Ca = 1.9 ± 0.5,_Mn-Mg = 0.6,_Ca-Mg = 3.7,_Mn-Fe = 0.2,_Ca-Fe = 2.8,_Mn-Sr = 9.7,_Ca-Sr = 2.15,_Mn-Ba = 4.0,_Ca-Ba = 1.4,validating the theoretical predictions given byLippmann in his pioneering 1980's paper. Thestrictly thermodynamic equilibrium model is not onlyable to match both the measured porewater andcarbonate solid-solution composition, but also topredict that the porewater pH, pe, alkalinity, anddissolved Mn, Fe, and S concentrations arecontrolled by the authigenic mineral bufferingassemblage mackinawite-greigite-rhodochrosite. Ourmodel is only compatible with the idea of ACRformation with typical composition (X_Mnbetween 70–75%) in the topmost sediment layerwhich, however, needs a major source ofMn_aq ^II. This is provided by reduction ofparticulate Mn oxides precipitated in significantamounts in the water column upon major inflow eventsin the Baltic Sea. The model enables also to set upscenarios of changing environmental conditions, e.g.,to predict the non-linear response of the carbonatesolid-solution composition to changes in Mn loading,alkalinity and salinity of the sediment-watersystem. The results suggest that the major andespecially minor element contents (Sr, Mg, Ba) inauthigenic carbonates can be applied as anenvironmental paleoproxy.     

Hochtemperatur-Plagioklas im Meteorit von Oldenburg

Zusammenfassung Der Plagioklas im Meteorit von Oldenburg (10. 9. 1930) zeigt Hochtemperaturoptik, die damit auch für weitere Chondrite wahrscheinlich ist. Zusammensetzung ist An₁₁, 2V = 60 1/2°, = 1,5365, Auslöschungsschiefe 7 1/2°, Winkel zwischen und der 0-Stelle der Auslöschung 24°, Winkel zwischen [001] und = 20°. Anteil 6%, Verzwillingung sehr eng nach dem Albit- und Periklingesetz. Die Indikatrix wird mit den bisherigen Werten für die Hochtemperaturoptik verglichen.     

An elevated temperature X-ray study of synthetic disordered Na-K alkali feldspars

The temperature dependence of cell parameters for three disordered, synthetic alkali feldspars (Or₁₉, Or₃₈, and Or₁₀₀) has been determined up to 1,000 °C. The samples show no change in composition or degree of Si-Al disorder during the experiments. The triclinic-monoclinic inversion in the sample of composition Or₁₉ occurs at 560 °±10 °C and is accompanied by changes in the rates of expansion of a, b and c; the rate for a increases and those for b and c decrease above the inversion. The b and c parameters in Or₁₀₀ show small decreases with increasing temperature and this may be due to thermal motion effects causing a contraction of cell directions that are fully expanded at room temperature. Calculation of the thermal expansion ellipsoids for the monoclinic phases shows that the major expansion coefficients (₁) for all three samples are more than an order of magnitude greater than the intermediate (₂) and minor (₃) coefficients. Thus the thermal expansion of these phases is dominated by that of ₁ which makes an angle of 22 ± 4 ° with+a; this orientation is parallel to that of the short M-OA2 bonds. The thermal expansion mechanism for monoclinic, disordered alkali feldspars may involve tilting within the framework releasing compression along this direction and allowing the M-OA2 bonds to show high expansion rates. The stretching of the crankshaft units, which are parallel to a, may only play a subordinate role in controlling the expansion of the feldspar framework.     

The role of hydrogen bonding in the thermal expansion and dehydration of brushite,di-calcium phosphate dihydrate

The unit-cell and atomic parameters of perdeuterated brushite have been extracted from Rietveld analysis of neutron powder diffraction data within the temperature range 4.2 to 470 K. The thermal expansion of brushite is anisotropic, with the largest expansion along the b axis due principally to the effect of the O(1)···D(4) and O(3)···D(2) hydrogen bonds. Expansion along the c axis, influenced by the Ow1···D(5) interwater hydrogen bond, is also large. The high temperature limits for the expansion coefficients for the unit-cell edges a, b and c are 9.7(5) × 10^–6, 3.82(9) × 10^–5 and 5.54(5) × 10^–5 K^–1, respectively, and for the cell volume it is 9.7(1) × 10^–5 K^–1. The angle displays oscillatory variation, and empirical data analysis results in = 1.28(3) × 10^–6sin(0.0105 T) K^–1, within this temperature range. The evolution of the thermal expansion tensor of brushite has been calculated between 50 T 400 K. At 300 K the magnitudes of the principal axes are ₁₁ = 50(6) × 10^{–6 K–1}, ₂₂ = 26.7(7) × 10^–6 K^–1 and ₃₃ = 7.0(5) × 10^–6 K^–1. The intermediate axis, ₂₂, is parallel to b, and using IRE convention for the tensor orthonormal basis, the axes ₁₁ and ₃₃ have directions equal to (–0.228, 0, –0.974) and (–0.974, 0, 0.228) respectively. Under the conditions of these experiments, the onset of dehydration occurred at temperatures above 400 K. Bond valence analysis combined with assessments of the thermal evolution of the bonding within brushite suggests that dehydration is precipitated through instabilities in the chemical environment of the second water molecule.     

Granulite facies amphibole and biotite equilibria,and calculated peak-metamorphic water activities

Samples located near the Oregon Dome anorthosite massif in the south-central Adirondack Mountains, New York contain the fluid-buffering mineral assemblages: amphibole + clinopyroxene + orthopyroxene + quartz or biotite + quartz + orthopyroxene + K-feldspar. These rocks were metamorphosed under granulite-facies conditions (T=725°–750°C, P=7.5 kbar) during the Grenville orogeny. The Mg-rich nature of amphiboles, micas, and pyroxenes allow accurate calculation of water activities because corrections for the effects of solid solution are relatively small. The activity of water was low during the peak of granulite-facies metamorphism, with H₂O0.15±0.14. Wollastonite occurrences indicate that the CO₂ was low (<0.3) in nearby rocks, demonstrating that large quantities of CO₂ did not infiltrate in a pervasive manner. The combination of low H₂O with low CO₂ is consistent with the hypothesis that magmatic processes were dominant, generating dry, fluid-absent conditions.Abbreviations fi Fugacity of species i in a fluid - Xi mole fraction of component i in a phase - T temperature - P lithostatic pressure - P _F fluid pressure - _i ^x activity of component i phase X     

Röntgenuntersuchung der wasserfreien Sulfate der dreiwertigen Metalle Eisen,Chrom und Gallium

Zusammenfassung Wasserfreies Eisen(III)sulfat, Fe₂(SO₄)₃, existiert in zwei Modifikationen. Nach Einkristallaufnahmen kristallisiert die eine wahrscheinlich in Raumgruppe (a_rh=8,791±0,004 Å, =55°52±2; Z=2), die andere in Raumgruppe C _2h ⁵ –P2₁/n (a=8,296±0,002 Å, b=8,515±0,002 Å, c=11,60±0,002 Å, =90°30; Z=4). Von Cr₂(SO₄)₃ und Ga₂(SO₄)₃ konnten für die rhomboedrischen Modifikationen, die isotyp zu jener von Fe₂(SO₄)₃ sind, aus Pulveraufnahmen die Gitterkonstanten bestimmt werden.

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Summary Anhydrous iron(III)sulfate exists in two modifications. From single-crystal work, one of the modifications crystallizes probably in space group (a_rh=8.791±0.004 Å, =55°52±2; Z=2), whereas the other in space group C _2h ⁵ –P2₁/n (a=8.296±0.002 Å, b=8.515±0.002 Å, c=11.60±0,002 Å, =90°30; Z=4). The lattice constants of the rhombohedral modifications of Cr₂(SO₄)₃ and Ga₂(SO₄)₃, which are isomorphous with rhombohedral Fe₂(SO₄)₃, have been determined from powder photographs.

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Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet.     

Über Strontioginorit,eine neue Ginorit-Varietdt aus dem Zechsteinsalz

Zusammenfassung Strontioginorit (Sr, Ca)₂B₁₄O₂₃ 8 H₂O mit Sr: Ca1,3:0,7 tritt in gut ausgebildeten Kristallen im Alteren Steinsalz von Reyershausen bei Göttingen auf. Es ergaben sich folgende Daten : ₀ = 12,85₀ Å,b ₀ = 14,48 Å,c ₀, = 12,85₅, Å, = 101° 35, RaumgruppeP 2_I/a,Z = 4, Dichte=2,25 gcm^–3,n = 1,512,n _/b = 1,524,n //[101] = 1,577.     

Thermal expansion,heat capacity,and entropy of MgO at mantle pressures

The pressure dependence of the Raman spectrum of forsterite was measured over its entire frequency range to over 200 kbar. The shifts of the Raman modes were used to calculate the pressure dependence of the heat capacity, C _v, and entropy, S, by using statistical thermodynamics of the lattice vibrations. Using the pressure dependence of C _v and other previously measured thermodynamic parameters, the thermal expansion coefficient, , at room temperature was calculated from = K _S (T/P) _S C _V/TVK _T, which yields a constant value of ( ln / ln V)_T= 6.1(5) for forsterite to 10% compression. This value is in agreement with ( ln / ln V)_T for a large variety of materials.At 91 kbar, the compression mechanism of the forsterite lattice abruptly changes causing a strong decrease of the pressure derivative of 6 Raman modes accompanied by large reductions in the intensities of all of the modes. This observation is in agreement with single crystal x-ray diffraction studies to 150 kbar and is interpreted as a second order phase transition.     

The pyroxmangite-rhodonite transformation for the MnSiO3 composition

The polymorphic transformation between synthetic pyroxmangite and rhodonite of MnSiO₃ composition has been reversibly bracketed in the presence of water at 3 kbar (between 425 ° and 450 ° C), 6 kbar (between 475 ° and 525 ° C), 20 kbar (between 500 ° and 900 ° C), 25 kbar (between 800 ° and 900 ° C) and 30 kbar (between 900 ° and 1,000 ° C), using standard cold-seal pressure vessels and piston cylinder apparatus. Oxygen fugacities buffered by the bomb walls and piston-cylinder cell assemblies sufficed to keep manganese in the divalent state. Pyroxmangite of MnSiO₃ composition is shown to be the high-pressure, low-temperature polymorph with respect to rhodonite of the same composition. It is a stable phase at atmospheric pressure below 350–405 ° C.X-ray data for synthetic pyroxmangite are presented. The unit-cell parameters (a₀=6.717(2) Å, b₀=7.603(1)Å, c₀=17.448(5) Å, =113 °50(1), = 82 °21(2), =94 °43(1); space group P-1) give a unit-cell volume (807.5(0.3) ų) which, in accordance with other recent least squares lattice refinements of hydrothermally synthesized material, is slightly smaller than that obtained by single-crystal work on anhydrously synthesized material.Application of the present results to natural rocks is severely restricted due to the great variety and extent of cationic substitutions observed in natural pyroxenoids. The univariant polymorphic transformation determined for the MnSiO₃ composition is thus replaced in natural systems by a divariant field in which pyroxmangite and rhodonite of differing composition will stably coexist.     

Eine Differenzmethode zur Erhöhung der Meßgenauigkeit und Erweiterung des Meßbereiches normaler Drehkompensatoren

Zusammenfassung Eine Differenzmethode zur Erhöhung den Genauigkeit der Messung von optischen Gangunterschieden durch Drehkompensatoren und Erweiterung von deren Mcßbereich wind beschrieben und durch Beispiele geprüft und erläutert.Der Vorteil dieses Verfahrens liegt in der erreichbaren Genauigkeit der Bestimmung kleiner und großer , die meist haher liegt als die der direkten Ermittelung durch Kompensation auf . = 0.Bei kleinen und großen , kann durch Messung einer Summe von Gangunterschieden oder eines Restgangunterschiedes anstatt des im Meßpräparat vorliegenden die Messung stets in den besten Meßbereich des jeweils vorliegenden Kompensators gerückt werden. Darüberhinaus sind höhere, durch Kompensatoren mit kleinerem Meßbereich ebenso genau bzw. nosh genauer bestimmbar. Es muß nun durch einen Quarzkeil oder einen underen Kompensator die ungefähre Lage der Kompensationsstelle auf = 0 ermittelt werden.Unter Verwendung monoehromatischen Lichtes können auch in der Additionsstellung von Meßpraparat und Kompensator ebensogut und genau bestimmt werden wie in der bisher traditionell bevorzugten Subtraktionsstellung.     

Cornetite: Modulated densely-packed Cu2+ oxysalt

Summary The crystal structure of cornetite, Cu₃(PO₄)(OH)₃, orthorhombic, a = 10.854(1), b = 14.053(3), c = 7.086(2), Å, V = 1080.8(3) ų, Z = 8, space group Pbca, has been refined to an R-index of 3.9% for 1231 observed reflections (I > 3I), measured with MoK X-radiation on an automated four-circle diffractometer. The structure consists of edge sharing zig-zag chains of distorted octahedra, cross-linked by edge-sharing octahedral dimers into complex octahedral layers. Adjacent layers are corner-linked together by neighbouring octahedra and PO₄ tetrahedra into a densely-packed heteropolyhedral framework, in which the phosphate tetrahedra share edges with the octahedral dimers. The polyhedral layers exhibit a commensurate modulation that results from the interaction between local relaxation of Jahn-Teller distorted octahedra and the long-range requirements of translational periodicity.

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Cornetit: Ein moduliertes, dicht gepacktes Oxosalz des zweiwertigen Kupfers

Zusammenfassung Die Kristallstruktur des Cornetits, Cu₃(PO4)(OH)3, orthorhombisch, a = 10,854(1), b = 14,053(3), c = 7,086(2,) Å, V = 1080,8(3) ų, Z = 8, Raumgruppe Pbca, wurde mit 1231 beobachteten Röntgenreflexen (I > 3I), die mit MoK-Strahlung auf einem automatischen Vierkreis-Diffraktometer gesammelt worden waren, auf einen R-Wert von 3,9% verfeinert. Die Struktur besteht aus kantenverknüpften Zickzack-Ketten verzerrter Oktaeder, die über kantenverknüfte Oktaeder-Dimere zu komplizierten Oktaederschichten verbunden sind. Benachbarte Schichten sind über Ecken durch benachbarte Oktaeder und PO₄-Tetraeder zu einem dichtgepackten, heteropolyedrischen Gerüst verknüpft, in welchem die Phosphattetraeder mit den Oktaeder-Dimeren Kanten gemeinsam haben. Die Polyederschichten zeigen eine kommensurable Modulierung, die aus der Wechselwirkung zwischen der lokalen Relaxation von Jahn-Teller-verzerrten Oktaedern und den Forderungen der translatorischen Periodizität über größere Entfernungen resultiert.

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With 5 Figures     

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.     

The crystal structure of trigonite,Pb3Mn(AsO3)2(AsO2OH)

Summary The mineral trigonite crystallizes in the monoclinic space groupPn–C _s ² witha ₀=7.26,b ₀=6.78,c ₀=11.09Å; =91.5°,Z=2. The structure was determined from 1250 X-ray intensities collected on an automatic two circle Weissenberg-type diffractometer. The final residual isR=6.5% using anisotropic temperature factors for Pb, Mn and As, and isotropic temperature factors for O.The structure consists of MnO₆ octahedra, sharing all six oxygens with arsenite groups to form a framework. The Pb atoms are attached to this framework with Pb–O distances2.23Å. One oxygen, bound only to an As atom, is interpreted as the donor for a hydrogen bond of 2.75Å.

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Die Kristallstruktur des Trigonits, Pb₃Mn(AsO₃)₂(AsO₂OH)

Zusammenfassung Das Mineral Trigonit kristallisiert monoklin, RaumgruppePn–C _s ² ,a ₀=7,26,b ₀=6,78,c ₀=11,09Å; =91,5°;Z=2. Die Strukturermittlung erfolgte anhand von 1250 Röntgenintensitäten, die auf einem automatischen Zweikreis-Weissenbergdiffraktometer gesammelt wurden. Mit anisotropen Temperaturfaktoren für Pb, Mn und As sowie isotropen für die O-Atome ergibt sich einR-Wert von 6,5%.Die MnO₆-Oktaeder werden über die sechs Sauerstoffe mit Arsenitgruppen zu einem dreidimensionalen Gerüst verknüpft. Über Pb-O-Abstände2,23 Å sind die Pb-Atome in dieses Gerüst eingebaut. Ein Sauerstoff, nur an ein As-Atom gebunden, wird als Donator einer H-Brücke von 2,75 Å interpretiert.

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With 2 Figures