The structures of orthorhombic GdAlO3 and GdFeO3 perovskites have been refined at room temperature and pressure using single-crystal x-ray diffraction and their equations of state have been measured to pressures of 7.95 and 7.58 GPa, respectively. Both structures are distorted through the tilting and distortion of the octahedra. GdAlO3 isless distorted than GdFeO3 with an average Al–O–Al tilt angle of 156.42(16)° compared to an average Fe–O–Fe tilt angle of 147.10(10)° in GdFeO3. Both the FeO6 octahedra and GdO12 sites in GdFeO3 are more distorted than those in GdAlO3. Neither perovskite exhibits any phase transitions throughout the pressure range studied. A fit of a third-order Birch–Murnaghan equation of state to the P–V data yields values of KT0 = 191(1) GPa and for GdAlO3 and KT0 = 182(1) GPa and for GdFeO3. Analysis of the unit cell parameter data shows that [100] is least compressible in both compounds and that GdFeO3 compresses more isotropically than GdAlO3. The compressional moduli for the unit cell parameters of GdFeO3 are Ka0 = 188(3) GPa, Kb0 = 181(1) GPa and Kc0 = 177(2) GPa, with , and , compared with Ka0 = 234(5) GPa, Kb0 = 151(2) GPa and Kc0 = 205(1) GPa, with , and for GdAlO3. There is no significant change in the pseudocubic unit cell parameters with pressure in GdFeO3 whereas they converge in GdAlO3. In particular, the ac and bc are predicted to merge by 12 GPa, signifying a possible transition from orthorhombic to tetragonal symmetry.

The crystal structure of Ag-excess fizélyite from the Van Silver mine, just north of Squamish, British Columbia, Canada, was studied on the basis of X-ray-diffraction data collected from an untwinned single crystal. The structure was refined to R 1 = 0.041 in space group P2 1 /n, with unit-cell parameters a 19.2767(6), b 13.2345 (4) (Ag2) and two split cation sites (Ag1 and M2) in our sample, fizélyite is isostructural with ramdohrite, CdAg 5.5 Pb 12 Sb 21.5 S 48 . The structure of fizélyite contains chains of edge-sharing SbS 6 octahedra connected by chains of alternating M1S 6 (M1 = Pb + Sb) and SbS 6 octahedra, forming slabs parallel to (100). The slabs of octahedra are linked by distorted AgS 4 tetrahedra, M2S 6 octahedra, and PbS 8 polyhedra. The excess Ag in our fizélyite is mostly situated at the Ag2 site, and is likely responsible for the splitting of the Ag1 and M2 sites.Keywords: fizélyite, ramdohrite, andorite, sulfosalt, crystal structure, single-crystal X-ray diffraction, Ag excess. SommAiReNous avons étudié la structure cristalline de la fizélyite contenant un excédent de Ag par diffraction X sur monocristal; l'échantillon non maclé provient de la mine d'argent Van, au nord de Squamish, en Colombie-Britannique, Canada. L'affinement a atteint un résidu R 1 de 0.041 dans le groupe spatial P2 1 /n, et les paramètres réticulaires sont: a 19.2767(6), b 13.2345(4),

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Abstract-Calcite crystals within the Kaibab limestone in Meteor Crater, Arizona, are examined to understand how calcite is deformed during a meteorite impact. The Kaibab limestone is a silty finegrained and fossiliferous dolomudstone and the calcite crystals occur as replaced evaporite nodules with impact-induced twinning. Twinning in the calcite is variable with deformational regimes based on abundances of crystals with twins and twin densities within crystals. The twins are similar to those that are seen in low tectonically deformed regimes. Low levels of shock are inferred from minor peak broadening of the X-ray diffraction patterns (XRD) of the calcite crystals. In addition, electron spin resonance (ESR) spectroscopy data also indicates low shock levels (<3.0 GPa). Quantitative shock pressures and correlation between the XRD and ESR results are poor due to the inferred low shock levels in conjunction with the analytical error associated in calculation of the shock pressures.

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