Multipole-refined charge density study of diopside at ambient conditions     

R. Bianchi  A. Forni  R. Oberti 《Physics and Chemistry of Minerals》2005,32(8-9):638-645

The experimental multipole electron density, ρ(r), of diopside was derived from high-resolution single-crystal diffraction at room temperature. Its topological analysis revealed predominantly ionic Si–O bonding, as found in electron density studies of other silicates. In particular, the non-bridging Si–O bonds are slightly less ionic in character than the bridging Si–O bonds. The Ca–O and Mg–O bonds are classified as pure closed-shell ionic interactions. An analysis of –∇²ρ(r) showed the presence of maxima around the oxygen atoms, associated to lone pairs domains that are involved in bonds with the surrounding ions. Calculation of atomic basins gave net charges of –1.56(12), 3.11(17), 1.79(13) and 1.88(18) e for O (averaged), Si, Ca and Mg atoms, respectively. O···O interactions between the O atoms at the vertices of the SiO₄ tetrahedron were also detected from the topological analysis of ρ(r), and indicate a cooperative interaction among the lone pairs of neighbouring oxygen atoms. All these results were also confirmed by periodic restricted Hartree–Fock (RHF) calculations. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.  相似文献   

Remediation of TCE-contaminated groundwater using zero valent iron and direct current: experimental results and electron competition model     

Ji-Won Moon  Hi-Soo Moon  Heonki Kim  Yul Roh 《Environmental Geology》2005,48(6):805-817

The objectives of this study are to design an optimal electro-enhanced permeable reactive barrier (E2PRB) system for the remediation of trichloroethylene (TCE)-contaminated water using zero valent iron (ZVI) and direct current (DC) and to investigate the mechanisms responsible for TCE degradation in different ZVI-DC configurations. A series of column experiments was conducted to evaluate the effect of different arrangements of electrodes and ZVI barriers in the column on the TCE removal capacity (RC). In twelve different combinations of ZVI and/or DC application in the test columns, the rate of reductive dechlorination of TCE was improved up to six times with simultaneous application of ZVI and DC compared to that using ZVI only. The most effective arrangement of electrode and ZVI for TCE removal was the column set with ZVI and a cathode installed at the down gradient. Based on the electrokinetic study for the column systems with only DC input, single acid front movement could explain different RCs. An enhanced dechlorination rate of TCE using E2PRB systems, compared to a conventional PRB system, was observed, and is considered to be attributed to more electron sources: (1) external DC, (2) electrolysis of water, (3) oxidation of ZVI, (4) oxidation of dissolved Fe²⁺, (5) oxidation of molecular hydrogen at the cathode, and (6) oxidation of Fe²⁺ in mineral precipitates. Each of these electron sources was evaluated for their potential influencing the TCE RC through the electron competition model and energy consumption. A strong correlation between the quantity of electrons generated, RC, and the energy-effectiveness was found.  相似文献   

岩石破裂中的电子发射   总被引：34，自引：10，他引：34       下载免费PDF全文

郭自强  周大庄  施行觉  马福胜  席道瑛  程纯杰  周志文 《地球物理学报》1988,31(5):566-571

利用G-M计数器和塑料闪烁体探测器在花岗岩单轴压缩破裂实验中首次记录到电子发射,电子能量分别为0.05McV和0.35MeV量级。根据这一结果提出了岩石破裂中出现可见光及其它电磁辐射的理论解释。  相似文献   

钙稀土氟碳酸盐系列矿物新规则堆垛结构的透射电镜研究   总被引：3，自引：0，他引：3       下载免费PDF全文

杨光明  潘兆橹 《地质科学》1994,29(4):393-398

采用现代透射电镜,研究我国西南某地产出的钙稀土氟碳酸盐矿物,又发现8种新的B_mS_n型规则混层组分和4种未曾报道的微多型。电子衍射和高分辨晶格象研究揭示了新规则堆垛结构特征及衍生体之间的结构取向关系。阐明了它们是由两个端员矿物-氟碳铈矿(B)和直氟碳钙铈矿(S)的结构单元层沿c轴方向以不同比例有序堆垛而成,因而导致了矿物组分和结构的不均一性。  相似文献   

Y—Ba—Cu—O系高Tc超导材料的电子衍射分析     

吴秀玲  赵文霞 《地球科学》1989,14(4):407-412

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ELF isosurface maps for the Al2SiO5 polymorphs     

J. B. Burt  G. V. Gibbs  D. F. Cox  N. L. Ross 《Physics and Chemistry of Minerals》2006,33(2):138-144

This study examines the electron localization function (ELF) isosurfaces of the Al₂SiO₅ polymorphs kyanite, sillimanite, and andalusite to see how differences in coordination and geometry of the cations and anions affect the ELF isosurfaces. Examination of the ELF isosurfaces indicates that their shapes are dependent on the coordination and geometry of the oxygen atoms and are not sensitive to coordination of the surrounding cations. Of the 18 crystallographically distinct oxygen atoms in the Al₂SiO₅ polymorphs, 13 are bonded to two aluminum atoms and one silicon atom (Al₂–O–Si) and are associated with two different ELF isosurface shapes. The shape of the ELF isosurface is dependent on the distance at which the oxygen atom lies from a plane defined by the three surrounding cations: at a distance greater than 0.2 Å the ELF can be defined as horseshoe-shaped and at a distance less then 0.2 Å it can be described as concave hemispherical. This feature is also seen in the ELF isosurfaces for the oxygens bonded to three aluminum atoms (Al₃–O) where the isosurfaces can be defined as trigonally toroidal and uniaxially trigonally toroidal. The changes in the ELF isosurfaces for the three coordinated oxygens are also indicative of changes in hybridization. The ELF isosurface for the two-fold coordinated oxygen (Al–O–Si) has a large mushroom-shaped isosurface along the Al–O bond and a concave hemispherical isosurface along the Si–O. The four-fold coordinated oxygen (Al₄–O) contains two concave hemispherical isosurfaces along the shorter Al–O bonds and a banana-shaped isosurface, which encompasses the longer Al–O bonds. In addition, this study shows the homeomorphic relationship between the ELF isosurfaces and electron density difference maps with respect to number and arrangement of domains.  相似文献   

Characteristics and genesis of hematite in Chinese loess and paleosol sequences： Mineral genetic restriction for magnetic susceptibility as paleoclimate proxy and iron geochemistry     

Tianhu CHEN Huifang XU Qiaoqin XIE Jun CHEN Junfeng JI Hualu LU Xiaoyong WANG 《中国地球化学学报》2006,25(B08):279-280

Hematite is an important iron oxide mineral in loess-paleosol sequences in central China. Investigation of the mineralogical characteristics, genetic mechanism and relationship of hematite with other iron oxides and Fe-bearing minerals will help understand the geochemical process before and after eolian deposit, paleocliamte significance of magnetic susceptibility and reconstruct paleoclimate in central China. So, hematite and related minerals of the loess and paleosol units from Chinese Loess Plateau were investigated using optical microscope, X-ray powder diffraction （XRD）, scanning electron microscopy （SEM）, and high-resolution transmission microscopy （HRTEM）. The results show that there are five genetic types of hematite in loess-paleosol sequences of central China： （1） weathering of Fe-bearing silicate minerals, for instance, chlorite, will release iron that is precipitated as aggregates of hematite nano-crystals on mineral surfaces; （2） hematite combined with eolian magnetite grains that resulted from partial oxidation of magnetite, even though the partial oxidation may occur in the original area; （3） phase transformation from eolian goethite to hematite; （4） hematite formed on the edge and surface of maghemite because of dissolution and hematite recrystallization; and （5） eolian detrial hematite. The hematite formed from chemical weathering of Fe-bearing silicates with nanoporous texture because of dehydration from iron hydroxide is the most important genetic mechanism. It is proposed that the fact that hematite was formed from chemical weathering of Fe-bearing silicates is a main reason for the redness in paleosol units. However, too intense pedogenesis and high amounts of precipitation will promote oxidation of eolian magnetite and maghemite dissolution, which may result in the decreasing of magnetic susceptibility.  相似文献   

Electron microprobe dating of monazite from high-T shear zones in the São José de Campestre Massif, NE Brazil     

Zorano Srgio de Souza  Jean-Marc Montel  Simone Maria Lima Costa Gioia  Maria Helena Bezerra Maia de Hollanda  Marcos Antonio Leite do Nascimento  Emanuel Ferraz Jardim de S  Venerando Eustquio Amaro  Mrcio Martins Pimentel  Jean-Marc Lardeaux  Michelle Veschambre 《Gondwana Research》2006,9(4):441-455

The easternmost domain of the Borborema Province, northeastern Brazil, presents widespread, extensional-related high-temperature metamorphism during the Brasiliano (=Pan-African) orogeny. This event reached the upper amphibolite to granulite facies and provoked generalized migmatization of Proterozoic metapelitic rocks of the Seridó Group and tonalitic to granodioritic orthogneisses of the Archean to Paleoproterozoic basement. We report new geochronological data based on electron microprobe dating of monazite from metapelitic migmatite and leuconorite within the high-T shear zones that make up the eastern continuation of the huge E–W Patos shear belt. These data were also constrained by using the Sm–Nd isotopic systematic on garnet from a syntectonic alkaline granite and two garnet-bearing leucosomes. The results suggest an age of about 578 to 574 Ma for the peak of the widespread high-T metamorphism. This event is best recorded by Sm–Nd garnet-whole rock ages. The U–Th–Pb isotopes on monazite of the metapelitic migmatite show a younger thermal event at 553 ± 10 Ma. When compared to the Sm–Nd garnet-whole rock ages, the U–Th–Pb electron probe monazite ages seem to record an event of slightly lower temperatures after the peak of the high-T metamorphism. This may reflect the difference in the isotopic behavior of the geochronological methods employed. Otherwise, the U–Th–Pb ages on monazites could indicate an event not yet very well defined. In anyway, this paper reveals the partial or even complete re-opening and resetting of the U–Th–Pb isotopic system produced by the action of low-T Ca-rich fluid.  相似文献   

Minerals at high pressure. Mechanics of compression from quantum mechanical calculations in a case study: the beryl (Al<Subscript>4</Subscript>Be<Subscript>6</Subscript>Si<Subscript>12</Subscript>O<Subscript>36</Subscript>)     

Mauro Prencipe  Fabrizio Nestola 《Physics and Chemistry of Minerals》2007,34(1):37-52

The Bader topological analysis has been applied to ab initio computed electron densities of beryl, in order to clarify its mechanism of compression. Full structural optimization and total energy (E) calculations were performed at different cell volumes (V _c). The pressure at each volume and the equation of state were estimated from the first and second derivatives of the resultant E(V _c) curve. The total (negative) potential energy of the crystal, sum of both attractive and repulsive electrostatic terms, was found to systematically decrease (i.e., it moved to more negative values) up to the highest pressure considered (28.4 GPa), indicating that interelectronic and internuclear repulsions are not the only terms controlling the compressibility, at least in the pressure range investigated. Electronic kinetic energy increases as the cell volume is reduced, leading to a parallel increase of the total energy. Both structure at equilibrium and compressibility are therefore due to the balance between the opposing kinetic and potential energy terms. The Bader theory has been used to identify the topological atoms within the structure and to calculate their properties, with particular attention to the forces driving the structural relaxation at high pressure. On a qualitative basis, the obtained results are expected to be transferable to the discussion of compressibility of other mineral phases.  相似文献   

Genesis and geological significance of sulfide bearing mafic enclaves and host syenite in Heishishan,East Kunlun: Evidence from geochronology,mineralogy, geochemistry and Sr-Nd-Hf isotopesSCIEI北大核心CSCD     

李治华  李碧乐  王斌  孙亚明  史雨凡  于润涛 《岩石学报》2023,(3):742-762

黑石山铜铅锌矿床位于东昆仑造山带中段的五龙沟地区,矿区内的石英二长岩-正长岩发育有暗色微粒包体,本研究在包体中发现了硫化物。锆石U-Pb定年显示,正长岩形成于239.4±1.0Ma,具有富Si和K,贫Mg、Cr、Ni,明显的Eu负异常,富集大离子亲石元素、亏损高场强元素,较为富集的Sr-Nd-Hf同位素特征。暗色微粒包体由斜长石和角闪石组成,可见角闪石堆晶,贫硅、富钙、铝、碱和铁,Mg#值为38.37,具有明显的Eu负异常,轻重稀土分馏弱。结合宿主正长岩和暗色包体的矿物成分相似性和岩相学特征,本文认为暗色微粒包体与正长岩来自同一个岩浆房,属于同源岩浆包体,是岩浆房早期分离结晶相,被中酸性岩脉携带上升至正长岩熔体中,一起侵位至浅部地壳。综合岩石地球化学、同位素和矿物成分,本文认为正长岩是下地壳含水镁铁质岩石在压力较低条件下部分熔融的产物。暗色微粒包体中发育硫化物,且包体岩浆的硫含量远高于正长岩岩浆,指示岩浆房的早期分离结晶相带走了硫,使残余熔体贫硫。  相似文献