Zeolites in the Granitic Rocks of Chugoku District, Southwest Japan

Ca-zeolites such as laumontite, stilbite and chabazite were found in the granitic rocks of both magnetite and ilmenite series of late Cretaceous to Tertiary age developed widely in the Chugoku district. These zeolites occur (1) in veins of various scale, (2) replacing plagioclase of the host granitic rocks, and (3) in pegmatitic druse. Mineralogy were investigated by X-ray powder diffraction method, the optical microscope, the scanning electron microscopy and the electron microprobe. Based on the mode of occurrence and the associated minerals, laumontite and stilbite in veins and replacing plagioclases are concluded to be formed from hydrothermal solutions filling open fractures which have been formed under the paleo-stress field after the solidification stage of the host granitic rocks. Probable formation condition of laumontite and stilbite was estimated as follows; 200-250°C(temperature), 0.5-1.0 Kb(P total) and 20-40 bar(max Pco )

Crystal structure of post-perovskite-type CaIrO3 reinvestigated: new insights into atomic thermal vibration behaviors

Single crystals of the title compound, the post-perovskite-type CaIrO3 [calcium iridium(IV) trioxide], have been grown from a CaCl2 flux at atmospheric pressure. The crystal structure consists of an alternate stacking of IrO6 octahedral layers and CaO8 hendecahedral layers along [010]. Chains formed by edge-sharing of IrO6 octahedra (point-group symmetry 2/m..) run along [100] and are interconnected along [001] by sharing apical O atoms to build up the IrO6 octahedral layers. Chains formed by face-sharing of CaO8 hendecahedra (point-group symmetry m2m) run along [100] and are interconnected along [001] by edge-sharing to build up the CaO8 hendecahedral layers. The IrO6 octahedral layers and CaO8 hendecahedral layers are interconnected by sharing edges. The present structure refinement using a high-power X-ray source confirms the atomic positions determined by Hirai et al. (2009) [Z. Kristallogr. 224, 345–350], who had revised our previous report [Sugahara et al. (2008). Am. Mineral. 93, 1148–1152]. However, the displacement ellipsoids of the Ir and Ca atoms based on the present refinement can be approximated as uniaxial ellipsoids elongating along [100], unlike those reported by Hirai et al. (2009). This suggests that the thermal vibrations of the Ir and Ca atoms are mutually suppressed towards the Ir...Ca direction across the shared edge because of the dominant repulsion between the two atoms

カイセキホウ ト XAFSホウ オ ヘイヨウ シタ フキソク コウゾウ カイセキ : α-AgIガタ コウゾウ ノ チョウ イオン ドウデン キコウ

The Debye-waller factors determined by diffraction and XAFS experiments provide important information about the thermal vibration and disordered structure. The statistical distribution of Ag in α-AgI and superionic conduction mechanism have been discussed based on the effective one-particle potential, probability density function and effective pair potential. The disordered nature of α-AgI is due to the thermal motion and the probability of finding mobile Ag ions at saddle point is a few percent in α-AgI

The Tricks of the Chameleon. Unexpected Symmetry of the Diffraction Pattern

International audienceThe first step in the structure solution process is the determination of candidate space groups on the basis of the symmetry of the diffraction pattern, in particular through the analysis of the reflection conditions. Sometimes it may happen that the diffraction pattern is indexed in an alternative setting of the space group, in which the reflection conditions appear different. The discrepancy between the observed reflection conditions and those published in the standard setting of space groups may lead the investigator to erroneously assume his sample is less symmetric than it actually is. After discussing a case from the literature where tetragonal samples were incorrectly described as orthorhombic due to an unusual indexing of the diffraction pattern, we present an example in which diffractions from a pyrite sample were indexed in the Pb3 setting of the space group, instead of the standard Pa3 setting, where the large set of strong violations of reflection conditions with respect to those of the standard setting could have been interpreted as a signature of symmetry lowering to P213. The structure being well-known, the real origin of the apparent violation