Crystal data on 1M and 2M2 lepidolites

A coarse-grained, colourless lepidolite from a pegmatite of the Elba Island (Italy) has been examined. X-ray powder-diffraction and single-crystal patterns reveal the presence of the 1M and 2M₂ polymorphs, for wich cell parameters are given. On the basis of the optical and X-ray data the same composition for both the polymorphs is inferred. From the chemical analysis data of the whole micaceous material the following formula has been computed: (Ca_0,01Na_0,06K_0,92Rb_0,06) (Al_1,27Mg_0,01Li_1,75) (Si_3,36Al_0,64)O₁₀ (F_1,53OH_0,47). The crystal structure of this mica has been studied by means of one-dimensional Fourier projections on c^* and several interesting structural parameters were derived. Among them the mean tetrahedral rotation results to be about 11° for both the polymorphs: a value (quite similar to those of the other trioctahedral micas with K⁺ as interlayer cation) wich does not confirm Radoslovich's hypothesis that lepidolites should have a symmetry of the tetrahedral layers very close to the perfect hexagonality. Finally a new hypothesis on the structure of the 2M₂ polymorph consistent with such a proved ditrigonal symmetry of the basal oxygens arrangement in the lepidolites is pointed out.Notations O_bas basal oxygen atoms of the (Al, Si)O₄ tetrahedra. - O_ap apical oxygen atoms of the (Al, Si)O₄ tetrahedra. - b _tetr b dimension which the tetrahedral sheet would assume if unconstrained. - b _obs observed value of b. - c _oct ^* thickness of the octahedral sheet. - c _tetr ^* thickness of the tetrahedral sheet. - average tetrahedral rotation from ideal hexagonal symmetry. - separation of two O_bas sheets in contact with the interlayer cation. - O_ap-Si-O_bas angle. This research was supported by Consiglio Nazionale delle Ricerche, Roma.     

Hydrogen bonding and vibrational properties of hydroxy groups in the crystal lattice of dioctahedral clay minerals by means of first principles calculations

The hydroxy groups of the crystal lattice of dioctahedral 2:1 phyllosilicates were investigated by means of quantum-mechanical calculation. The standard Kohn-Sham self-consistent density functional theory (DFT) method was applied using the generalized gradient approximation (GGA) with numerical atomic orbitals and double-zeta polarized functions as basis set. Isomorphous cation substitution of different cations in the octahedral and tetrahedral sheet was included along with several interlayer cations reproducing experimental crystal lattice parameters. The effect of these substitutions and the interlayer charge on the hydroxyl group properties was also studied. These structures represent different cation pairs among Al³⁺, Fe³⁺ and Mg²⁺ in the octahedral sheet of clays joined to OH groups. The geometrical disposition of the OH bond in the crystal lattice and the hydrogen bonds and other electrostatic interactions of this group were analyzed. The frequencies of different vibrational modes of the OH group [(OH), (OH) and (OH)] were calculated and compared with experimental data, finding a good agreement. These frequencies depend significantly on the nature of cations which are joined with, and the electrostatic interactions with, the interlayer cations. Besides, hydrogen-bonding interactions with tetrahedral oxygens are important for the vibrational properties of the OH groups; however, also the electrostatic interactions of these OH groups with the rest of tetrahedral oxygens within the tetrahedral cavity should be taken into account. The cation substitution effect on the vibration modes of the OH groups was analyzed reproducing the experimental behaviour.Dr. V. Botella passed away last February     

Compressional behaviour of CaNiSi2O6 clinopyroxene: bulk modulus systematic and cation type in clinopyroxenes

A single-crystal of composition CaNiSi₂O₆ (space group C2/c) was investigated at high pressure up to about 7.8 GPa by X-ray diffraction. The unit-cell parameters were measured at 18 different pressures. The P-V data were fitted by a third-order Birch-Murnaghan equation of state V₀=435.21(1) ų, K ₀=117.6(3) GPa and K^=6.4(1). The linear axial compressibilities _a, _b, _c and a sin are 2.14(1), 3.00(1), 2.43(1) and 1.63(1) × 10–3 GPa^–1. Comparing the compressibility data with other CaM1Si₂O₆ pyroxenes we suggest that the empirical K × V = constant relationships are followed in C2/c pyroxenes only if the same valence electron character is shared.     

Refinement of the structure of ζ-Nb2O5 and its relationship to the rutile and thoreaulite structures

Summary The crystal structure of -Nb₂O₅, space groupC2/c, a 12.740(2),b 4.8830(6),c 5.5609(6)Å, 105.02(1)°, Z 4, has been refined toR 1.6% for 457 observed reflections (MoK). The coordination polyhedron of the niobium atom is a distorted octahedron; the crystal structure consists of two-octahedron-thick, rutile-like layers separated by crystallographic shear (CS) planes. Relative to the rutile structure, these planes are indexed (101) and adjacent layers are related by the CS vector <a/6b/2c/2>. Members of the thoreaulite-foordite series have topologically identical two-octahedron-thick (101) sheets; however, here the CS vector Zusammenfassung Die Kristallstruktur des -Nb₂O₅, Raumgruppe C2/c, a 12,740(2),b 4,8830(6),c 5,5609(6) Å, 105,02(1)°,Z 4, wurde mit 457 beobachteten Reflexen (MoK) aufR 1,6% verfeinert. Das Koordinationspolyeder des Niobiumatoms ist ein verzerrtes Oktaeder; die Kristallstruktur besteht aus Rutil-artigen Schichten, die zwei Oktaeder dick sind und von kristallographischen Scher-(CS-)flächen getrennt werden. In bezug auf die Rutilstruktur haben diese Flächen die Indizes (101) und benachbarte Schichten sind durch den CS-Vektor <a/6b/2c/2> verknüpft. Die Glieder der Thoreaulith-Foordit-Reihe haben idente (101)-Schichten einer Dicke von zwei Oktaedern; indessen bewirkt hier der CS-Vektor <a/2> _r gekoppelt mit dem Translationsvektor <1,5c> _r die Einlagerung von tetragonal-antiprismatischen Lücken zwischen benachbarte Schichten.

---

---

With 4 Figures     

Aluminous orthopyroxene: Order-disorder,thermodynamic properties,and petrologic implications

Orthopyroxene has two tetrahedral sites, designated A and B, and two octahedral sites, M1 and M2. Crystallographic studies of synthetic and natural orthopyroxenes (opx) suggest that the tetrahedral Al is ordered nearly completely in the B site, but the octahedral Al disorders between M1 and M2 sites with a preference for M1. If the aluminum avoidance principle is obeyed, then the tetrahedral Si-Al ordering limits the Al substitution in opx to 25 mol%, thus leading to an end-member stoichiometry of Mg₃Al₂Si₃O₁₂ instead of MgAl₂SiO₆.The enthalpy of formation of these two components has been deduced from the available phase equilibrium data. The thermodynamic properties of the opx solid solution approximates ideal solution behavior more closely when treated in terms of the components Mg₄Si₄O₁₂(QEn)-Mg₃Al₂Si₃O₁₂(Py) than when expressed in terms of the components Mg₂Si₂O₆-MgAl₂SiO₆. A model has been developed for the octahedral disordering of Al as function of temperature and composition. These data enable calculation of the configurational entropy and molar entropy of Al-opx; distinction has been made between the cases of completely random mixing of Al and Si in the tetrahedral B site, and of random mixing without violation of the aluminum avoidance principle. The second model yields entropy of the Mg₃Al₂Si₃O₁₂ end member which agrees almost exactly with the value derived from phase equilibrium data. The partial molal entropies of the Orthopyroxene components QEn and Py can be derived from these data; their implications with respect to the P-T slopes of Al₂O₃ isopleths for the equilibrium of Orthopyroxene with forsterite and spinel/garnet have been discussed.     

An experimental investigation of olivine morphology

Olivine crystals can adopt ten types of shape. Experimental crystallization of eight rock melts shows that there is a systematic change from polyhedral or granular olivines hopper olivines branching olivines randomly oriented chain olivines parallel-growth chain olivines chain+lattice olivines plate or feather olivines, with increase in cooling rate and with increase in degree of supercooling. This sequence involves changes from complete to progressively less complete crystals and from equant habit to elongate bladed habit (c>ab) to tabular habit (ac b). The sequence is not affected by the phase relations of the melt. The larger the olivine content of a melt the slower the cooling rate at which a particular olivine shape grows, whereas the lower the melt viscosity, the greater the cooling rate. Irrespective of the melt composition, comparable crystal shapes grow at the same degrees of supercooling. By comparison of the shapes of olivine crystals in experiments with those in rocks of similar composition, it is possible to deduce the cooling rate through the olivine crystallization interval and the approximate degree of supercooling at which the olivine crystals nucleated and grew in the rocks. The various shapes of skeletal olivines in many picrites, olivine-rich basalts and the Archaean spinifex rocks are not due to rapid cooling, but to rapid olivine growth caused by the high normative olivine content of the magma.     

A new oxygen-deficient perovskite phase Ca(Fe<Subscript>0.4</Subscript>Si<Subscript>0.6</Subscript>)O<Subscript>2.8</Subscript> and phase relations along the join CaSiO<Subscript>3</Subscript>–CaFeO<Subscript>2.5</Subscript> at transition zone conditions

A new oxygen-deficient perovskite with the composition Ca(Fe_0.4Si_0.6)O_2.8 has been synthesised at high-pressure and -temperature conditions relevant to the Earths transition zone using a multianvil apparatus. In contrast to pure CaSiO₃ perovskite, this new phase is quenchable under ambient conditions. The diffraction pattern revealed strong intensities for pseudocubic reflections, but the true lattice is C-centred monoclinic with a=9.2486 Å, b=5.2596 Å, c=21.890 Å and =97.94°. This lattice is only slightly distorted from rhombohedral symmetry. Electron-diffraction and high-resolution TEM images show that a well-ordered ten-layer superstructure is developed along the monoclinic c* direction, which corresponds to the pseudocubic [111] direction. This unique type of superstructure likely consists of an oxygen-deficient double layer with tetrahedrally coordinated silicon, alternating with eight octahedral layers of perovskite structure, which are one half each occupied by silicon and iron as indicated by Mössbauer and Si K electron energy loss spectroscopy. The maximum iron solubility in CaSiO₃ perovskite is determined at 16 GPa to be 4 at% on the silicon site and it increases significantly above 20 GPa. The phase relations have been analysed along the join CaSiO₃–CaFeO_2.5, which revealed that no further defect perovskites are stable. An analogous phase exists in the aluminous system, with Ca(Al_0.4Si_0.6)O_2.8 stoichiometry and diffraction patterns similar to that of Ca(Fe_0.4Si_0.6)O_2.8. In addition, we discovered another defect perovskite with Ca(Al_0.5Si_0.5)O_2.75 stoichiometry and an eight-layer superstructure most likely consisting of a tetrahedral double layer alternating with six octahedral layers. The potential occurrence of all three defect perovskites in the Earths interior is discussed.     

Synthetic bayleyite,Mg2[UO2(CO3)3]·18H2O: Thermochemistry,crystallography and crystal structure

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     

Corundum,Cr-muscovite rocks at O'Briens,Zimbabwe: the conjunction of hydrothermal desilicification and LIL-element enrichment — geochemical and isotopic evidence

Monomineralic domains of chlorite, corundum and Cr muscovite coexist over a kilometer scale within ultramafic schists of the Harare greenstone belt (2.73 Ga). This exotic lithological association includes the conjunction of some of the most aluminous (Al₂O₃88 wt%) and potassic (K₂O10 wt%) rocks known. The paragenetic sequence developed from chloritecorundumcorundum+ diaspore: Cr muscovite variably overprinted both the corundum and chloritite domains. Terminal stages were marked by sporadic production of andalusite+quartz, and finally margarite.Chlorite (Cr₂O₃=0.31–2.65 wt%), corundum (0.79–2.66 wt%), and diaspore are all Cr-rich varieties. The chromian (Cr₂O₃3.86 wt%) paragonitic muscovite incorporates up to 17% of the paragonite molecule, and significant Mg and Fe substitutions.The suite of rocks are characterized by chondritic Ti/Zr ratios (–x=107), systematically enhanced Cr (up to 14000 ppm) and Ni (up to 1200 ppm) abundances, low levels of the alteration-insensitive incompatible elements Th, Ta, Nb. Chlorite, corundum and Cr muscovite represent progressive stages in the incremental metasomatic alteration of a komatiite precursor. Mass balance calculations, constrained by the isochemical behaviour of Ti, Zr and Hf reveal that the komatiite chloritite transformation involved volumetric contractions of 60% by hydrothermal leaching of Si, Fe, Mn, Ca and Na. Reaction of chloritite to corundum involved further volumetric reductions of 50% due to essentially quantitative loss of Si, Fe, Mn, Mg, K and Ca. Conversion of corundum to muscovite required additions of Si, K, Fe, Mn, Mg, Rb and Ba at 50–200% dilation. K, Rb, Ba, Li and Cs are enriched by up to 2×10³ over background abundances in ultramafic rocks, and the suite is also enriched in B, Se, Te, Bi, As, Sb and Au. REE were extensively leached during chloritite-corundum stages, whereas LREE additions accompany development of muscovite. Ti, Zr, Hf and Al were all concentrated by selective leaching of mobile components, but absolute additions of Al accompanied development of the corundum domains due to Al precipitation in response to depressurization.Corundum ( ¹⁸O=3.5–4.8), muscovite ( ¹⁸O=6.7–7.5) and chlorite (4.5–5.6) are isotopically uniform and formed at 380–520° C from a fluid where ¹⁸O=5.6–6.9. The corundum is ¹⁸O depleted relative to either igneous or anatectic counterparts (O_cor=7.6–8.2), or to gibbsitic laterites ( ¹⁸O=12–17).Previous genetic schemes involving metamorphism of exhalites or bauxite, or Si-undersaturation of magmas, can all be ruled out from the data. The chloritite, corundum, Cr-muscovite association represents sequential alteration products of ultramafic rocks by high temperature, low pH hydrothermal solutions carrying LIL-elements, and in which excursions of pH and/or degree of quartz undersaturation account for the mineralogical transitions. A deep level acid epithermal system, or fluid advection across steep inverted thermal gradients in a thrust regime could account for required hydrothermal conditions.     

An exsolution silica-pump model for the origin of myrmekite

Myrmekite, as defined here, is the microscopic intergrowth between vermicular quartz and modestly anorthitic plagioclase (calcic albite-oligoclase), intimately associated with potassium feldspar in plutonic rocks of granitic composition. Hypotheses previously invoked in explanation of myrmekite include: (1) direct crystallization; (2) replacement; (3) exsolution. The occurrence of myrmekite in paragneisses and its absence in rocks devold of discrete grains of potassium feldspar challenge those hypotheses based on direct crystallization or replacement. However, several lines of evidence indicate that myrmekite may in fact originate in response to kinetic effects associated with the exsolution of calcic alkali feldspar into discrete potassium feldspar and plagioclase phases. Exsolution of potassium feldspar system projected from [AlSi₂O₈] involves the exchange CaAlK_-1Si_-1, in which the AlSi_-1 tetrahedral couple is resistant to intracrystalline diffusion. By contrast, diffusion of octahedral K proceeds relatively easily where it remains uncoupled to the tetrahedral exchange. We suggest here that where the ternary feldspar system is open to excess silica, the exchange reaction that produces potassium feldspar in the ternary plane is aided by the net-transfer reaction K+Si=Orthoclase, leaving behind indigenous Si that reports as modal quartz in the evolving plagioclase as the CaAl component is concomitantly incorporated in this same phase. Thus silica is pumped into the reaction volume from a silica reservoir, a process that enhances redistribution of both Si and Al through the exsolving ternary feldspar.     

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.     

The crystal structure of sarkinite,Mn2AsO4(OH)

Summary Sarkinite is a basic manganese arsenate, Mn₂AsO₄(OH). The lattice parameters are:a=12.779 (2) Å,b=13.596 (2) Å,c=10.208 (2) Å, =108°53 (6). Space groupP2₁/a,Z=16. The crystal structure has been solved by direct methods from three-dimensional X-ray diffractometer data and refined by least-squares methods toR=0.052 for 3519 independent reflections. The crystal structure is built up by a three-dimensional framework of MnO₄(OH)₂ octahedra, MnO₄(OH) trigonal bipyramids and AsO₄ tetrahedra, as found in wagnerite. Isotypy of sarkinite with triploidite is confirmed.

---

Die Kristallstruktur des Sarkinits, Mn₂AsO₄(OH)

Zusammenfassung Die Kristallstruktur des basischen Manganarsenates Sarkinit, Mn₂AsO₄(OH), mit den Gitterkonstantena=12,779 (2) Å,b=13,596 (2) Å,c=10,208 (2) Å, =108°53 (6). RaumgruppeP2₁/a,Z=16, wurde mit dreidimensionalen Röntgendiffraktometermessungen durch direkte Methoden gelöst und nach dem kleinste-Quadrate-Verfahren verfeinert (R=0,052 für 3519 unabhängige Reflexe). Die Struktur besteht aus einem dreidimensionalen Gerüst aus MnO₄(OH)₂-Oktaedern, trigonalen Bipyramiden von MnO₄(OH) und AsO₄-Tetraedern wie in Wagnerit. Die Isotypie von Sarkinit mit Triploidit wurde bestätigt.

---

---

With 1 Figure     

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.     

Hauptdolomit — Sedimentary and paleogeographic models (Norian,Northern Calcareous Alps)

In previous work, relationsships between carbonate petrographic features and geochemical parameters were used in the development of a sedimentary model for Hauptdolomit. It was found useful to categorize the various facies subtypes into eight main facies units which correspond to environments ranging from supratidal to subtidal.Especially significant for stratigraphy and paleogeography are recurring, calcareous, subtidal intercalations (eastern Lechtal Alps), which interfinger with dolomitic to slightly calcareous transitional facies including bituminous marls (Seefeld facies). The latter facies is interpreted to be of lower intertidal to near-shore subtidal origin, because of its lateral and vertical association with subtidal facies on the one hand and with typical intertidal, dolomitic facies on the other hand.Three stratigraphic subdivisions (Lower Hd., Middle Hd., Upper Hd.) may be distinguished by correlating transgressional-regressional sequences.The Middle Hd./Upper Hd. transgression is especially useful for paleogeographic reconstructions. A shallow tongue-shaped lagoon encroached from the Dachstein area into the Lechtal Alps. It is partially obscured tectonically by the Inntal nappe. The lagoonal outline is accentuated by the transitional facies belt (subtidal to lower intertidal) which includes Seefeld facies.

---

Zusammenfassung In früheren Arbeiten wurde ein Sedimentationsmodell des Hauptdolomits mit Hilfe von karbonatpetrographischen Merkmalen und geochemischen Parametern entwickelt. Dabei war eine Gliederung der verschiedenen Faziestypen in acht Haupteinheiten hilfreich, welche Gezeiten-bis Lagunenmilieus (supratidal to subtidal) entsprechen.Besonders signifikant für Stratigraphie und Paläogeographie sind wiederkehrende, kalkige, lagunäre Zwischenschaltungen (östliche Lechtaler Alpen), welche sich mit einer dolomitischen bis schwach kalkigen Übergangsfazies einschließlich bituminösen Mergeln verzahnen (Seefelder Fazies). Wegen ihrer lateralen und vertikalen Verbindung mit lagunärer Fazies einerseits und typisch dolomitischer Watt-Fazies andererseits, stellen wir die Seefelder Fazies in den Bereich Niederwatt bis küstennahe Lagune (lower intertidal to near shore subtidal).Durch Korrelation von Transgressions-/Regressions-Folgen können drei stratigraphische Unterteilungen unterschieden werden (Unterer, Mittlerer und Oberer Hauptdolomit).Die Mittlerer/Oberer Hauptdolomit-Transgression ist besonders nützlich für paläogeographische Rekonstruktionen. Eine seichte zungenförmige Lagune dehnte sich ausgehend vom Dachsteingebiet bis in die Lechtaler Alpen aus. Sie ist teilweise tektonisch von der Inntaldecke überfahren. Der lagunäre Umriß wird hervorgehoben durch einen Gürtel mit Übergangs-(subtidal to lower intertidal) und Seefeldfazies.

---

Résumé Dans les travaux antérieurs on a développé un modèle sédimentaire de la Hauptdolomit à l'aide de caractères pétrographiques des carbonates et de paramètres géochimiques. Il s'est trouvé utile de grouper les différents types de facies en huit unités principales, qui correspondent à des milieux de marée jusqu'à ceux de lagune (supratidal à subtidal). - Sont particulièrement significatifs pour la stratigraphie et la paléogéographie les retours d'intercalations calcaires et lagunaires qui s'engrènent avec un facies de transition dolomitique à faiblement calcaire avec inclusions de marnes bitumineuses (facies de Seefeld). A cause de leurs connexions latérales et verticales avec des facies lagunaires dolomitiques d'une part, et avec des facies de Watt dolomitiques typiques, les facies de Seefeld sont interprétés comme des milieux de bas-fond inférieur allant jusqu'à des lagunes proches de la côte (lower intertidal to near-shore subtidal). Par la voie de corrélation de transgression/régression, on peut distinguer trois subdivisions stratigraphiques (Hauptdolomite inférieure, moyenne, supérieure). Pour la reconstruction paléogéographique, la transgression de la Hauptdolomite moyenne/supérieure se présente comme extrêmement utile. Une lagune peu profonde, en forme de langue, s'épanouissait à partir de la région de Dachstein jusqu'aux Alpes de la vallée de la Lech. Elle a été en partie recouverte tectoniquement par la nappe de la vallée de l'Inn. Le contour lagunaire est souligné par une ceinture des facies de transition (subtidal to lower intertidal), qui inclut aussi les facies de Seefeld.

---

- . 8 , - (supratidal to subtidal). , ( ), ( ). - , , (lower intertidal to near shore subtidal). : , . . . . (subtidal to lower intertidal).

     

Very high CO2 cordierite from Norwegian Lapland: Mineralogy,petrology, and carbon isotopes

The most CO₂-rich cordierite thus far encountered in nature with about 2.2 wt.% CO₂ and 0.3 wt.% H₂O occurs as large poikiloblasts in a strange non-foliated reaction rock that dissects well-foliated granulites being part of the classical Lapland granulite area described by Eskola. The cordierite is optically positive with the highest optic angle 2V _x (106°) and birefringence (– = 0.017) ever measured on natural cordierites, but it is also optically very heterogeneous due to secondary loss of CO₂ along fractures and zones paralleling the fluid-bearing channels. Based on the optical properties of the degassed Lapland cordierite and on literature data a ternary diagram is given, which shows the variations of this cordierite in 2V _x and birefringence as a function of channel-filling with both CO₂ and H₂O.Following Losert (1971) the cordierite coexists with calcite, a thus far unique mineral assemblage that is probably only stable at very high CO₂ pressures. In the present case, the of the cordierite (0.75) indicates, on the basis of literature data, a coexisting fluid with >0.95.The carbon isotope composition ¹³C of CO₂ in cordierite lies near –7, that of the calcite is slightly lighter than about –9. Thus, at least for the CO₂ in cordierite, a deep-seated origin may be possible.Based on the geologic occurrence it is speculated that the cordierite-bearing reaction rock could perhaps represent an annealed channel of late degassing in the granulitic lower crust.     

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).     

Use of the lattice parameter b 0 of dioctahedral illite/muscovite for the characterization of P/T gradients of incipient metamorphism

The P/T gradient or baric type of low-grade metamorphic terranes can be characterized on the basis of cumulative frequency curves of the lattice parameter b ₀ of dioctahedral micas (Sassi and Scolari 1974), which essentially reflects celadonite content and increases with pressure. The method is here applied to illite/muscovite of sub-greenschist (incipient metamorphism) and low-greenschist facies terranes from the marginal zones of the Swedish Caledonides, Swiss Alps and Venezuelan Andes, where the grade of metamorphism was determined on the basis of illite crystallinity.Complications in the determinations of b ₀ arising from (a) shifts in the spacing of the apparent 060 diffraction peaks of the illites due to the presence of inter-stratified expandable layers, and (b) persistence of more crystalline clastic micas are pointed out.In contrast to the earlier-reported decrease of b ₀ with progressive metamorphism at higher grades, b ₀ tends to increase with grade during incipient metamorphism: it is markedly lower in the diagenetic and low-grade anchimetamorphic grades in the Cambro-Silurian of the Caledonides of Jämtland, western Sweden (zone A), and the Lower Tertiary of the Helvetic zone of the Swiss Alps, than in the higher grade anchizone and epizone of the former terrane.Mean b ₀ values for the intermediate and highest (epizone) grades of the Swedish Caledonides are respectively 9.030 and 9.037 Å compared to the mean value of 9.035 Å for the medium-high pressure, Barrovian-type, terrane of Otago, N.Z. Mean b ₀ of 9.005 Å for the mainly epizonal slates of the Venezuelan Andes lies between those for the low-pressure terranes of Bosost ( 8.992 Å), and the low-medium pressure terrane of northern New Hampshire (9.010 Å). These baric estimates agree well with those for the metamorphic facies series at higher grade produced by the same events.Cumulative b ₀ curves are concluded to be useful for the characterization of P/T gradients of incipient metamorphism, particularly in the higher grade part of the anchizone and the epizone.     

Dispersive Particle Transport: Identification of Macroscale Behavior in Heterogeneous Stratified Subsurface Flows

Dispersive mass transport processes in naturally heterogeneous geological formations (porous media) are investigated based on a particle approach to mass transport and on its numerical implementation using LPT3D, a Lagrangian Particle Tracking 3D code. We are currently using this approach for studying microscale and macroscale space–time behavior (advection, diffusion, dispersion) of tracer plumes, solutes, or miscible fluids, in 1,2,3-dimensional heterogeneous and anisotropic subsurface formations (aquifers, petroleum reservoirs). Our analyses are based on a general advection-diffusion model and numerical scheme where concentrations and fluxes are discretized in terms of particles. The advection-diffusion theory is presented in a probabilistic framework, and in particular, a numerical analysis is developed for the case of advective transport and rotational flows (numerical stability of the explicit Euler scheme). The remainder of the paper is devoted to the behavior of concentration, mass flux density, and statistical moments of the transported tracer plume in the case of heterogeneous steady flow fields, where macroscale dispersion occurs due to geologic heterogeneity and stratification. We focus on the case of perfectly stratified or multilayered media, obtained by generating many horizontal layers with a purely random transverse distribution of permeability and horizontal velocity. In this case, we calculate explicitly the exact mass concentration field C(x, t), mass flux density field f(x, t), and moments. This includes spatial moments and dispersion variance ² _x (t) on a finite domain L, and temporal moments on a finite time scale T, e.g., the mass variance of arrival times ² _T (x). The moments are related to flux concentrations in a way that takes explicitly into account finite space–time scales of analysis (time-dependent tracer mass; spatially variable flow through mass). The multilayered model problem is then used in numerical experiments for testing different ways of recovering information on tracer plume migration, dispersion, concentration and flux fields. Our analyses rely on a probabilistic interpretation that emerges naturally from the particle approach; it is based on spatial moments (particle positions), temporal moments (mass weighted arrival times), and probability densities (both concentrations and fluxes). Finally, as an alternative to direct estimations of the flux and concentration fields, we formulate and study the Moment Inverse Problem. Solving the MIP yields an indirect method for estimating the space–time distribution of flux concentrations based on observed or estimated moments of the plume. The moments may be estimated from field measurements, or numerically computed by particle tracking as we do here.     

Vorkommen und Entstehung von „Salz-Schirmen“ im Tuz Gölü („Salzsee“), Türkei

Zusammenfassung Aus randlichen Teilbecken des Tuz Gölü (Salzsee), Türkei, werden bis zu 40 cm große, über dem Wasserspiegel des Salzbeckens liegende Salzschirme beschrieben, deren einzelne Anwachsstreifen verschiedenen Wasserständen bei der Evaporation des Beckens entsprechen. Die Schirmform kann durch bevorzugtes Horizontal-Wachstum der NaCl-Kristalle in der obersten Wasserschicht bei gleichzeitig sinkendem Wasserspiegel gedeutet werden. Ansatzpunkte für die Schirmbildung sind im Sediment steckende NaCl-inkrustierte Pflanzenstengel, die in das Becken eingeschwemmt wurden.

---

Occurrence and origin of Salt-umbrellas in the Tuz Gölü (Salt-Lake), Turkey

Salt umbrellas with a maximum diameter of 40 cm are a special form of NaCl growth. They occur above the water surface of evaporating Tuz Gölü (Salt Lake) in Central Anatolia, Turkey. The different growth rims of the umbrella correspond to the different water levels during evaporation of the basin.The umbrella-like shape is best to be explained by the fact that within the uppermost water layer (highest NaCl-concentration) NaCl-crystals grow preferentially in horizontal direction while the water level is steadily sinking.Small plant-stems having been brought into the basin and incrusted by NaCl act as crystallization centers for the formation of the umbrellas.

---

---

Herrn R. H. Okan, Direktor der Salzwerke von Yavsan Tuzlasi, sowie Herrn Georg Irion, Heidelberg, danke ich herzlich für die wertvolle Mithilfe bei der Probenahme.     

Synthesis and some properties of iron- and vanadium-bearing kyanites, (Al,Fe3+)2SiO5and (Al,V3+)2SiO5

Iron- and vanadium-bearing kyanites have been synthesized at 900 and 1100° C/20 kb in a piston-cylinder apparatus using Mn₂O₃/Mn₃O₄- and MnO/Mn-mixtures, respectively, as oxygen buffers. Solid solubility on the pseudobinary section Al₂SiO₅-Fe₂SiO₅(-V₂SiO₅) of the system Al₂O₃-Fe₂O₃(V₂O₃)-SiO₂ extends up to 6.5 mole% (14mole %) of the theoretical end member FeSiO₅(V₂SiO₅) at 900°C/20 kb. For bulk compositions with higher Fe₂SiO₅ (V₂SiO₅) contents the corundum type phases M₂O₃(M = Fe³⁺, V³⁺) are found to coexist with the Fe³⁺(V³⁺)-saturated kyanite solid solution plus quartz. The extent of solid solubility on the join Al₂SiO₅-Fe₂SiO₅ at 1 100°C was not found to be significantly higher than at 900° C. Microprobe analyses of iron bearing kyanites gave no significant indication of ternary solid solubility in these mixed crystals. Lattice constants a ₀, b ₀, c ₀, and V₀ of the kyanite solid solutions increase with increasing Fe₂SiO₅- and V₂SiO₅-contents proportionally to the ionic radii of Fe³⁺ and V³⁺, respectively, the triclinic angles ,, remain constant. Iron kyanites are light yellowish-green, vanadium kyanites are light green. Iron kyanites, (Al_1.87 Fe _0.13 ³⁺ )SiO₅, were obtained as crystals up to 700 m in length.