Twin laws of whewellite,CaC2O4·H2O. A structural and growth approach     

Dino Aquilano  Marinella Franchini-Angela 《Physics and Chemistry of Minerals》1981,7(3):124-129

Both natural and synthetic crystals of whewellite (CaC₂O₄·H₂O, sp.g. P2₁/c) occur commonly as twins. The geometrical, reticular and structural features of the most important twin law, twin plane (100), and the dubious law ( \(\overline {\text{1}} \) 01) were investigated. The strict application of the periodic bond chain (PBC) theory (Hartman and Perdok 1955) makes possible the identification of original composition planes (OCP). Following the OCP analysis it has been deduced that the energy necessary to produce a (100) twin is very low. This is evidenced by the easy reciprocal arrangement of the two crystal structures which can be shown in two slightly different ways, i.e., by a (100) reflection with a mean [0, 1/2, ?a ₀cosβ] translation and a weak relaxation (from 0.1 to 0.25 Å) of the common interface. In OCP an important role is played by water molecules. With regard to ( \(\overline {\text{1}} \) 01) twinning, the geometrical and reticular agreement is not matched by the structural situation. The structural and growth approach to the twin laws of whewellite therefore justifies the very common occurrence only of (100) twinned crystals.  相似文献   

Development and Application of 2D and 3D GRASS Modules for Simulation of Thermally Driven Slope Winds     

Marco Ciolli  Massimiliano de Franceschi  Roberto Rea  Alfonso Vitti  Dino Zardi  Paolo Zatelli 《Transactions in GIS》2004,8(2):191-209

The ability to manage and process fully three‐dimensional information has only recently been made available for a few Geographical Information Systems (GIS). An example of integrated and complementary use of 2D and 3D GRASS modules for the evaluation and representation of thermally induced slope winds over complex terrain is presented. The analytic solution provided by Prandtl (1942) to evaluate wind velocity and (potential) temperature anomaly induced by either diurnal heating or nocturnal cooling on a constant angle slope is adopted to evaluate wind and temperature profiles at any point over both idealised and real complex terrain. As these quantities depend on the slope angle of the ground and on the distance from the slope surface suitable procedures are introduced to determine the coordinate n of a point in the 3D volume measured along the direction locally normal to the terrain surface. A new GRASS module has been developed to evaluate this quantity and to generate a 3D raster file where each cell is assigned the value of the cell on the surface belonging to the normal vector. The application of the algorithm implemented in GRASS to an ideal valley and to a real valley close to the city of Trento in the Alps provides results in accordance with data reported in the literature. An extension of Prandtl's (1942) model to take into account humidity and evaporation processes on the soil is also proposed and implemented.  相似文献   

Theoretical growth morphology of whewellite CaC2O4·H2O     

Marinella Franchini-Angela  Dino Aquilano 《Physics and Chemistry of Minerals》1984,10(3):114-120

The morphological theory of Hartman and Perdok (1955, 1956) allows to deduce the character of a growth form {hkl} on the basis of structural data alone. Its application to the structure of whewellite leads to the identification of forms {100}, {010}, {021}, {011}, {12 \(\bar 1\) } and {121} which show during the growth a flat surface profile (flat forms F). These forms occur very frequently in the crystals we grew from pure aqueous solutions at supersaturation β≦1,90. Other forms, {001} and {10 \(\bar 1\) }, possibly show a double character (F or S, where S stays for related faces showing a stepped profile during the growth) according to the bonds assumed within some periodic bond chains (PBCs). Alternative ways of bonding water molecules lead to different structures of the same PBC. The different energy corresponding to these structures may explain the complex morphology of both natural and synthetic crystals grown at high β values.  相似文献   

Fast ion conduction character and ionic phase-transitions in disordered crystals: the complex case of the minerals of the pearceite–polybasite group     

L. Bindi  M. Evain  A. Pradel  S. Albert  M. Ribes  S. Menchetti 《Physics and Chemistry of Minerals》2006,33(10):677-690

The minerals of the pearceite–polybasite group, general formula (Ag,Cu)₁₆ M ₂S₁₁ with M = Sb, As, have been recently structurally characterized. On the whole, all the structures can be described as a regular succession of two module layers stacked along the c axis: a first module layer (labeled A), with general composition [(Ag,Cu)₆(As,Sb)₂S₇]²⁻, and a second module layer (labeled B), with general composition [Ag₉CuS₄]²⁺. In detail, in the B layer of the pearceite structure silver cations are found in various sites corresponding to the most pronounced probability density function locations of diffusion-like paths. We have shown for the first time that the observed structural disorder in the B layer is strongly related to the fast ion conduction character exhibited by these minerals. This paper reports an integrated XREF, DSC, CIS and EPMA study on all the members of the pearceite–polybasite group. DSC and conductivity measurements pointed out that the 222 members show ionic-transitions at 340 K (arsenpolybasite-222) and 350 K (polybasite-222), whereas the 221 members have transitions at lower temperature, that is, 310–330 K (arsenpolybasite-221) and 335 K (polybasite-221). For the 111 members (pearceite and antimonpearceite), the transition occurs below room temperature at 273 K. In situ single-crystal X-ray diffraction experiments showed that these minerals present the same high temperature structure and are observed at room temperature either in their high temperature (HT) fast ion conductivity form or in one of the low temperature (LT) fully ordered (222), partially ordered (221) or still disordered (111) forms, with transition temperatures slightly above or below room temperature. The pearceite–polybasite group of minerals can be considered as a homogeneous series with the same aristotype, fast ion conducting form at high temperature. Depending upon the Cu content, an ordering occurs with transition temperatures related to that content: the lower the Cu content, the higher the transition temperature from the fast ion conducting HT form to the non-ion conducting form.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.  相似文献   

Economic damages due to extreme precipitation during tropical storms: evidence from Jamaica     

Collalti  Dino  Strobl  Eric 《Natural Hazards》2022,110(3):2059-2086

Natural Hazards - This study investigates economic damage risk due to extreme rainfall during tropical storms in Jamaica. To this end, remote sensing precipitation data are linked to regional...  相似文献   

Merwinite-structured phases as a potential host of alkalis in the upper mantle     

Luca Bindi  Oleg G. Safonov  Dmitriy A. Zedgenizov 《Contributions to Mineralogy and Petrology》2015,170(2):1-11

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Sodium Silicates at the Boundary between the Transition Zone and the Lower Mantle: Compositional and Structural Patterns     

Matrosova  E. A.  Bobrov  A. V.  Tamarova  A. P.  Bindi  L.  Pushcharovsky  D. Yu.  Irifune  T. 《Doklady Earth Sciences》2020,491(1):150-154

Doklady Earth Sciences - The new results of experimental study of the Na2MgSiO4–Mg2SiO4 section of the SiO2–MgO–Na2O model system at 22–24 GPa and 1600–1900°C are...  相似文献   

Application-driven ground motion prediction equation for seismic hazard assessments in non-cratonic moderate-seismicity areas     

D. Bindi  F. Cotton  S. R. Kotha  C. Bosse  D. Stromeyer  G. Grünthal 《Journal of Seismology》2017,21(5):1201-1218

We present a ground motion prediction equation (GMPE) for probabilistic seismic hazard assessments (PSHA) in low-to-moderate seismicity areas, such as Germany. Starting from the NGA-West2 flat-file (Ancheta et al. in Earthquake Spectra 30:989–1005, 2014), we develop a model tailored to the hazard application in terms of data selection and implemented functional form. In light of such hazard application, the GMPE is derived for hypocentral distance (along with the Joyner-Boore one), selecting recordings at sites with vs30 ≥ 360 m/s, distances within 300 km, and magnitudes in the range 3 to 8 (being 7.4 the maximum magnitude for the PSHA in the target area). Moreover, the complexity of the considered functional form is reflecting the availability of information in the target area. The median predictions are compared with those from the NGA-West2 models and with one recent European model, using the Sammon’s map constructed for different scenarios. Despite the simplification in the functional form, the assessed epistemic uncertainty in the GMPE median is of the order of those affecting the NGA-West2 models for the magnitude range of interest of the hazard application. On the other hand, the simplification of the functional form led to an increment of the apparent aleatory variability. In conclusion, the GMPE developed in this study is tailored to the needs for applications in low-to-moderate seismic areas and for short return periods (e.g., 475 years); its application in studies where the hazard is involving magnitudes above 7.4 and for long return periods is not advised.  相似文献   

A vacancy‐rich,partially inverted spinelloid silicate, (Mg,Fe,Si)2(Si,□)O4, as a major matrix phase in shock melt veins of the Tenham and Suizhou L6 chondrites     

Chi Ma  Oliver Tschauner  Luca Bindi  John R. Beckett  Xiande Xie 《Meteoritics & planetary science》2019,54(9):1907-1918

A new high‐pressure silicate, (Mg,Fe,Si)₂(Si,□)O₄ with a tetragonal spinelloid structure, was discovered within shock melt veins in the Tenham and Suizhou meteorites, two highly shocked L6 ordinary chondrites. Relative to ringwoodite, this phase exhibits an inversion of Si coupled with intrinsic vacancies and a consequent reduction of symmetry. Most notably, the spinelloid makes up about 30–40 vol% of the matrix of shock veins with the remainder composed of a vitrified (Mg,Fe)SiO₃ phase (in Tenham) or (Mg,Fe)SiO₃‐rich clinopyroxene (in Suizhou); these phase assemblages constitute the bulk of the matrix in the shock veins. Previous assessments of the melt matrices concluded that majorite and akimotoite were the major phases. Our contrasting result requires revision of inferred conditions during shock melt cooling of the Tenham and Suizhou meteorites, revealing in particular a much higher quench rate (at least 5 × 10³ K s^?1) for veins of 100–500 μm diameter, thus overriding formation of the stable phase assemblage majoritic garnet plus periclase.  相似文献   

Phase Relations in the Model System SiO<Subscript>2</Subscript>–MgO–Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>: Evidence from the Results of Experiments in Petrologically Significant Sections at 12–24 GPa and 1600°C     

E. A. Matrosova  A. V. Bobrov  L. Bindi  T. Irifune 《Petrology》2018,26(6):588-598

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