Probable Space Group Research Articles

Synthesis and Properties of the Ba2PrWO6 Double Perovskite.

We report details on the synthesis and properties of barium praseodymium tungstate, Ba2PrWO6, a double perovskite that has not been synthesized before. Room-temperature (RT) powder X-ray diffraction identified the most probable space group (SG) as monoclinic I2/m, but it was only slightly distorted from the cubic structure. X-ray photoelectron spectroscopy confirmed that the initial (postsynthesis) material contained praseodymium in both 3+ and 4+ charge states. The former (Pr3+) disappeared after exposure to UV light at RT. Photoluminescence studies of Pr3+ revealed that Ba2PrWO6 is an insulator with a band gap exceeding 4.93 eV. Pressure-dependent Raman spectroscopy excluded the possibility of a phase transition up to 20 GPa; however, measurements between 8 and 873 K signified that there might be a change toward the lower symmetry SG below 200 K. Electron paramagnetic resonance spectra revealed the presence of interstitial oxygen which acts as a deep electron trap.

Kuvaevite, Ir5Ni10S16, a New Mineral Species, Its Associations and Genetic Features, from the Sisim River Placer Zone, Eastern Sayans

Abstract —Kuvaevite, ((Ir,Rh)5(Ni,Fe,Cu)10S16), forms small grains (up to 20 µm across) in globular inclusions hosted by grains of Os–Ir–(Ru) alloys (up to 0.5 mm) in ore occurrences along the Ko River in the Sisim placer zone, Eastern Sayans. Rh-bearing pentlandite or oberthürite (or both), the minerals of the laurite-erlichmanite series and Pt–(Pd)–Fe alloys are the main associated minerals. Kuvaevite is gray to brownish gray in color in reflected light. Its bireflectance is weak to absent. It is slightly pleochroic in gray to light brown shades, and slightly anisotropic, from gray to light yellow shades. Its calculated density is 6.37 g/cm3. According to results of microprobe analyses (n = 3) carried out using wavelength-dispersive spectrometry, WDS, the composition of kuvaevite is: Cu 5.94 (4.39–6.89), Ni 13.95 (13.80–14.24), Fe 10.95 (10.18–11.97), Co 0.07 (0.06–0.10), Ir 32.38 (32.19–32.73), Rh 7.27 (7.22–7.31), Pt 1.91 (1.67–2.06), Os 0.05 (0–0.09), Ru 0.05 (0.04–0.05), S 27.06 (26.77–27.41), total 99.63 wt.%. The empirical formulae calculated using the mean results of analyses are: (Ir3.22Rh1.35Pt0.19Ru0.01Os0.01)Σ4.78(Ni4.54Fe3.75Cu1.79Co0.02)Σ10.10S16.13 (WDS) and (Ir3.23Rh1.43Pt0.25)Σ4.91(Ni4.49Fe3.57Cu1.86Co0.06)Σ9.98S16.11 (SEM/EDS; n = 56). These are based on a total of 31 atoms according to structural data obtained for torryweiserite, the rhodium-dominant analogue. Kuvaevite forms solid-solution series with torryweiserite, tamuraite and ferrotorryweiserite, all these being isostructural. The symmetry of kuvaevite was determined using the synchrotron Laue microdiffraction; the results are in good agreement with the trigonal crystal system and give the following unit-cell parameters: a = 7.079(5) Å, c = 34.344(12) Å, V = 1490(2) Å3; Z = 3. The ratio c/a is 4.852. The probable space-group, R3m (#166), is based on structural results for torryweiserite. The strongest eight reflections in the X-ray diffraction pattern derived from the microdiffraction study [d in Å(hkl) (I)], are the following: 3.0530(201)(43), 3.0103(216)(100), 2.9962(1010)(53), 2.7991(205)(50), 2.4946(208)(31), 1.9208(3110)(41), 1.7697(410)(73), 1.7582(2016)(66). The results of the electron backscatter diffraction study (EBSD) of two kuvaevite crystals are well–indexed based on the R3m space group. Kuvaevite and related sulfides significantly vary in composition in the Ko River placer, in the entire Sisim zone, and in some other ore occurrences worldwide. Associations of platinum-group minerals observed in ore occurrences at Ko River and in the Sisim zone seem to be genetically related to bedrock zones of chromite-bearing ultramafic rocks (serpentinites) of the Lysanskiy complex. Kuvaevite and other minerals present in the polymineralic inclusions, hosted by Os–Ir–(Ru) alloys, formed from droplets of residual melt. This melt accumulated the “incompatible” elements, which could not be incorporated into the structure of the host alloy, including lithophile elements, chalcogens (S, Te), semimetals (As, Sb, Bi), base metals (Fe, Ni, Cu), as well as relatively low-temperature PGE species (Pt, Pd) and Rh. There are local data on metastable crystallization and undercooling of the silicate melt, as well as effective differentiation and fractionation of S and ore components during the crystallization of these inclusions. Kuvaevite is named after O.M. Kuvaev (1934–1975), a prominent geologist, geophysicist and writer.

Ferrotorryweiserite, Rh5Fe10S16, a New Mineral Species from the Sisim Placer Zone, Eastern Sayans, Russia, and the Torryweiserite–Ferrotorryweiserite Series

Ferrotorryweiserite, Rh5Fe10S16, occurs as small grains (≤20 µm) among droplet-like inclusions (up to 50 μm in diameter) of platinum-group minerals (PGM), in association with oberthürite or Rh-bearing pentlandite, laurite, and a Pt-Pd-Fe alloy (likely isoferroplatinum and Fe-Pd-enriched platinum), hosted by placer grains of Os-Ir alloy (≤0.5 mm) in the River Ko deposit. The latter is a part of the Sisim placer zone, which is likely derived from ultramafic units of the Lysanskiy layered complex, southern Krasnoyarskiy kray, Russia. The mineral is opaque, gray to brownish gray in reflected light, very weakly bireflectant, not pleochroic to weakly pleochroic (grayish to light brown tints), and weakly anisotropic. The calculated density is 5.93 g·cm–3. Mean results (and ranges) of four WDS analyses are: Ir 18.68 (15.55–21.96), Rh 18.34 (16.32–20.32), Pt 0.64 (0.19–1.14), Ru 0.03 (0.00–0.13), Os 0.07 (0.02–0.17), Fe 14.14 (13.63–14.64), Ni 13.63 (12.58–14.66), Cu 4.97 (3.42–6.41), Co 0.09 (0.07–0.11), S 29.06 (28.48–29.44), and total 99.66 wt.%. They correspond to the following formula calculated for a total of 31 atoms per formula unit: (Rh3.16Ir1.72Pt0.06Ru0.01Os0.01)Σ4.95(Fe4.48Ni4.11Cu1.38Co0.03)Σ10.00S16.05. The results of synchrotron micro-Laue diffraction studies indicate that ferrotorryweiserite is trigonal; its probable space group is R3¯m (#166) based on its Ni-analog, torryweiserite. The unit-cell parameters refined from 177 reflections are a = 7.069 (2) Å, c = 34.286 (11) Å, V = 1484 (1) Å3, and Z = 3. The c:a ratio is 4.8502. The strongest eight peaks in the X-ray diffraction pattern derived from results of micro-Laue diffraction study [d in Å(hkil)(I)] are 2.7950 (202¯5) (100); 5.7143 (0006) (60); 1.7671 (224¯0) (44.4); 3.0486 (202¯1) (39.4); 5.7650 (101¯2) (38.6); 2.5956 (202¯7) (37.8); 3.0058 (112¯6) (36.5); and 1.5029 (42¯ 2¯12) (35.3). Ferrotorryweiserite and the associated PGM crystallized from microvolumes of residual melt at late stages of crystallization of grains of Os- and Ir-dominant alloys occurred in lode zones of chromitites of the Lysanskiy layered complex. In a particular case, the residual melt is disposed peripherally around a core containing a disequilibrium association of magnesian olivine (Fo72.9–75.6) and albite (Ab81.6–86.4), with the development of skeletal crystals of titaniferous augite: Wo40.8–43.2En26.5–29.3Fs20.3–22.6Aeg6.9–9.5 (2.82–3.12 wt.% TiO2). Ferrotorryweiserite represents the Fe-dominant analog of torryweiserite. We also report occurrences of ferrotorryweiserite in the Marathon deposit, Coldwell Complex, Ontario, Canada, and infer the existence of the torryweiserite–ferrotorryweiserite solid solution in other deposits and complexes.

Tamuraite, Ir5Fe10S16, a New Species of Platinum-Group Mineral from the Sisim Placer Zone, Eastern Sayans, Russia

Tamuraite, ideally Ir5Fe10S16, occurs as discrete phases (≤20 μm) in composite inclusions hosted by grains of osmium (≤0.5 mm across) rich in Ir, in association with other platinum-group minerals in the River Ko deposit of the Sisim Placer Zone, southern Krasnoyarskiy Kray, Russia. In droplet-like inclusions, tamuraite is typically intergrown with Rh-rich pentlandite and Ir-bearing members of the laurite–erlichmanite series (up to ~20 mol.% “IrS2”). Tamuraite is gray to brownish gray in reflected light. It is opaque, with a metallic luster. Its bireflectance is very weak to absent. It is nonpleochroic to slightly pleochroic (grayish to light brown tints). It appears to be very weakly anisotropic. The calculated density is 6.30 g·cm−3. The results of six WDS analyses are Ir 29.30 (27.75–30.68), Rh 9.57 (8.46–10.71), Pt 1.85 (1.43–2.10), Ru 0.05 (0.02–0.07), Os 0.06 (0.03–0.13), Fe 13.09 (12.38–13.74), Ni 12.18 (11.78–13.12), Cu 6.30 (6.06–6.56), Co 0.06 (0.04–0.07), S 27.23 (26.14–27.89), for a total of 99.69 wt %. This composition corresponds to (Ir2.87Rh1.75Pt0.18Ru0.01Os0.01)Σ4.82(Fe4.41Ni3.90Cu1.87Co0.02)Σ10.20S15.98, calculated based on a total of 31 atoms per formula unit. The general formula is (Ir,Rh)5(Fe,Ni,Cu)10S16. Results of synchrotron micro-Laue diffraction studies indicate that tamuraite is trigonal. Its probable space group is R3m (#166), and the unit-cell parameters are a = 7.073(1) Å, c = 34.277(8) Å, V = 1485(1) Å3, and Z = 3. The c:a ratio is 4.8462. The strongest eight peaks in the X-ray diffraction pattern [d in Å(hkl)(I)] are: 3.0106(216)(100), 1.7699(420)(71), 1.7583(2016)(65), 2.7994(205)(56), 2.9963(1010)(50), 5.7740(102)(45), 3.0534(201)(43) and 2.4948(208)(38). The crystal structure is derivative of pentlandite and related to that of oberthürite and torryweiserite. Tamuraite crystallized from a residual melt enriched in S, Fe, Ni, Cu, and Rh; these elements were incompatible in the Os–Ir alloy that nucleated in lode zones of chromitites in the Lysanskiy layered complex, Eastern Sayans, Russia. The name honors Nobumichi Tamura, senior scientist at the Advanced Light Source of the Lawrence Berkeley National Laboratory, Berkeley, California.

On the fluoride-mediated synthesis and amine intercalation of large lamellar crystals of layered titanosilicate Na/K-JDF-L1

Fluoride-mediated synthesis in the inorganic hydrothermal system has been proposed for preparing large crystals of layered Na/K-JDF-L1 with lamellar morphology. The protonated JDF-L1 crystals derived from their layered precursors are structurally modified by 1,6-hexanediamine intercalation under mild hydrothermal conditions. All the materials mentioned are characterized by XRD, FESEM, EDX/ICP-AES, and TGA–DSC. It is concluded that the combination of fluorides with low alkalinity (pH ca.10.0) and crystallization temperature (200 °C) facilitates the oriented growth of metastable layered phase Na/K-JDF-L1, yielding regular lamellar crystals with square-sheet structure in two-dimensions of ca. 15 × 15 μm. Data on Na/K-JDF-L1 structure are presented for identification of the most probable tetragonal space group, P4212, corresponding to the highest crystallographic symmetry. It is also revealed that amine intercalation of relevant H-JDF-L1 by the hydrothermal process leads to the formation of layered titanosilicate materials with an ordered redistribution of the dominant interlayer space (d001) shifting from 10.674 to 15.620 A.

Kutnohorite CaMn(CO3)2 crystal growth at high pressure-temperature

High quality kutnohorite CaMn(CO3)2 single crystals up to 100 μm in size were successfully achieved under high pressure-temperature (P-T) conditions. Electron microprobe analyses revealed the average wt% of CaO was 25.98% and that of MnO was 32.88%, correspondingly well to the ideal formula of Ca1.0Mn1.0(CO3)2. Accurate crystalline structural data were determined from single-crystal X-ray diffraction (XRD), with the R3 space group and R3c space group used to refine the crystal structure of CaMn(CO3)2. The Ca-O and Mn-O bond lengths were slightly different when using the R3 space group, which were clearly distinguished from those in the dolomite structure. Therefore, R3c is the most probable space group for the CaMn(CO3)2 crystal structure. Thermogravimetric (TG) analysis and differential scanning calorimetry (DSC) showed that CaMn(CO3)2 decomposed from 620–750 °C, but only one endothermic peak was observed during the decomposition process. It indicated that the octahedral units in CaMn(CO3)2 have the same thermal stability due to the complete miscibility of Ca and Mn. The results of single crystal XRD and thermal analysis provided direct evidence that CaMn(CO3)2 has a calcitetype structure, not dolomite-type layered structure, which was in good agreement with the rigid model of rhombohedral carbonates.

Crystal structure of norsethite-type BaMn(CO3)2 and its pressure-induced transition investigated by Raman spectroscopy

Single crystals of norsethite-type carbonate BaMn(CO3)2 up to 200 μm in size were synthesized in a closed cavity under high pressure–temperature (P–T) conditions. Electron microprobe analyses revealed the composition of 49.00–49.09 wt% BaO and 22.66–22.74 wt% MnO, which correspond well to the ideal formula of Ba1.0Mn1.0(CO3)2. Accurate crystalline structural data were determined from single crystal X-ray diffraction (XRD). The $$R\overline{3} c$$ space-group with a doubled c-axis and $$R\overline{3} m$$ space-group were used to refine the crystal structure of BaMn(CO3)2. It is proved that $$R\overline{3} m$$ is the most probable space-group for the BaMn(CO3)2 crystal structure because no superstructure reflections were observed in the X-ray images. The unit cell parameters were identified to be a = 5.0827(2) A and c = 17.2797(10) A in the rhombohedral symmetry of the $$R\overline{3} m$$ space-group with a final R-value of 0.0184. High-pressure Raman spectroscopy was performed up to 10 GPa at room temperature, and Raman band shifts ( $$\frac{{{\text{d}}\nu_{i} }}{{{\text{d}}P}}$$ ) were quantified. Each Raman vibration underwent resolvable splitting and the corresponding $$\frac{{{\text{d}}\nu_{i} }}{{{\text{d}}P}}$$ showed a pronounced jump as the pressure reached 3.8 GPa arising from a pressure-induced transition.

Zincovelesite-6N6S, Zn3(Fe3+,Mn3+,Al,Ti)8O15(OH), a new högbomite-supergroup mineral from Jacupica mountains, Republic of Macedonia

A new mineral species zincovelesite-6N6S with the simplified formula Zn3(Fe3+,Mn3+,Al,Ti)8O15(OH) was discovered in the orogenetic zone related to the “Mixed Series” metamorphic complex near the Nežilovo village, Jacupica Mountains, Pelagonia mountain range, Republic of Macedonia. In oxide Zn-Fe-Mn ore, zincovelesite-6N6S forms lenticular aggregates up to 2 × 2 × 0.5 mm consisting of thin near-coplanar platelets up to 70 × 70 × 1 µm3 and associated with franklinite, gahnite, hetaerolite, zincochromite, ferricoronadite, baryte, As-rich fluorapatite, dolomite, Zn-bearing talc, almeidaite, hydroxycalcioromeite, zircon, quartz, and scheelite. In silicate-baryte zones of the metasomatic rock, uniaxial intergrowths of zincovelesite-6N6S with nežilovite are observed. The new mineral is opaque, black, with brownish-black streak. The lustre is strong submetallic to metallic. The micro-indentation hardness is 1118 kg/mm2 which corresponds to Mohs’ hardness ca. 6½. Zincovelesite-6N6S is brittle, with uneven fracture. No cleavage or parting is observed. The density calculated from the empirical formula is 5.158 g/cm3. In reflected light zincovelesite-6N6S is light grey. The reflectance values [Rmax/Rmin, % (λ, nm)] are: 17.1/13.4 (470), 16.5/12.8 (546), 16.2/12.6 (589), 15.6/12.2 (650). The IR spectrum shows the presence of OH groups. According to the Mossbauer spectrum, all iron is trivalent. The Mn K-edge XANES spectroscopy shows that Mn is predominantly or completely trivalent. The average chemical composition is (wt%; electron microprobe, H2O determined by gas chromatography of ignition products): MgO 0.97, CuO 0.50, ZnO 30.80, Al2O3 8.17, Mn2O3 21.31, Fe2O3 29.44, TiO2 5.28, Sb2O5 3.74, H2O 1.1, total 101.31. The empirical formula based on 16 O atoms is H1.05Zn3.26Mg0.21Cu0.05Fe3+3.18Mn3+2.32Al1.38Ti0.57Sb0.20O16. Zincovelesite-6N6S is trigonal, probable space group P-3m1, a = 5.902(2) A, c = 55.86(1) A, V = 1684.8(9) A3, Z = 6. The strongest lines of the powder X-ray diffraction pattern [d, A (I, %) (hkl)] are: 2.952 (62) (110), 2.881 (61) (1.0.16), 2.515 (100) (204), 2.493 (88) (1.1.12), 2.451 (39) (1.0.20), 1.690 (19) (304, 2.1.16), 1.572 (19) (2.0.28), 1.475 (29) (221). Zincovelesite-6N6S is the first Fe3+-dominant member of the hogbomite supergroup and, thus, can be considered as a parent species of a new mineral group. The rootname velesite is given for the discovery locality near the city of Veles.

Crystal structure prediction of rigid molecules.

A non-polarizable force field based on atomic multipoles fit to reproduce experimental crystal properties and ab initio gas-phase dimers is described. The Ewald method is used to calculate both long-range electrostatic and 1/r(6) dispersion energies of crystals. The dispersion energy of a crystal calculated by a cutoff method is shown to converge slowly to the exact Ewald result. A method for constraining space-group symmetry during unit-cell optimization is derived. Results for locally optimizing 4427 unit cells including volume, cell parameters, unit-cell r.m.s.d. and CPU timings are given for both flexible and rigid molecule optimization. An algorithm for randomly generating rigid molecule crystals is described. Using the correct experimentally determined space group, the average and maximum number of random crystals needed to find the correct experimental structure is given for 2440 rigid single component crystals. The force field energy rank of the correct experimental structure is presented for the same set of 2440 rigid single component crystals assuming the correct space group. A complete crystal prediction is performed for two rigid molecules by searching over the 32 most probable space groups.

Space Group Approximation of a Molecular Crystal by Classifying Molecules for Their Electric Potentials and Roughness on Their Inertial Ellipsoid Surface

In order to predict the most probable space group where a molecule crystallizes, it is assumed that molecular shape and electric potential distribution on the molecular surface are the main factors or predictors. However, to compare and classify molecules by these two factors seems to be very difficult for in general such different objects. Thus, in order to compare molecules, they are reduced to their inertial ellipsoid in which surface 26 equally spaced points were chosen where a roughness factor and an electric potential due to all atomic charges of the whole molecule are calculated. By this procedure, different molecules encoded by these two predictor vectors can be compared and classified, showing that molecules that crystallize in the same space group have more similar predictor vectors. This result opens the possibility to predict the more probable spatial group associated with a molecule.

Two types of adjacent dimer layers in the low-temperature phase of BaCuSi2O6

The low-temperature crystal structure of BaCuSi2O6has been investigated with high-resolution synchrotron x-ray and neutron powder diffraction techniques and has been found to be on average (ignoring the incommensurate modulation) orthorhombic, with the most probable space group Ibam. The Cu-Cu dimers in this material are forming two types of layers with distinctly different interatomic distances. Subtle changes also modify the partially frustrated interlayer Cu-Cu exchange paths. The present results corroborate the interpretation of low-temperature nuclear magnetic resonance and inelastic neutron scattering data in terms of distinct dimer layers. The experimentally determined low-temperature crystal structure of BaCuSi2O6is discussed in terms of its relation to the newer findings of theory and of the complementary experiments.

Two types of adjacent dimer layers in the low-temperature phase of BaCuSi2O6

The low-temperature crystal structure of ${\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}$ has been investigated with high-resolution synchrotron x-ray and neutron powder diffraction techniques and has been found to be on average (ignoring the incommensurate modulation) orthorhombic, with the most probable space group $Ibam$. The Cu-Cu dimers in this material are forming two types of layers with distinctly different interatomic distances. Subtle changes also modify the partially frustrated interlayer Cu-Cu exchange paths. The present results corroborate the interpretation of low-temperature nuclear magnetic resonance and inelastic neutron scattering data in terms of distinct dimer layers.

DAJUST: a suite of computer programs for pattern matching, space-group determination and intensity extraction from powder diffraction data

DAJUSTis the generic name of a software package for powder diffraction formed by the core programsAJUSTandSGAID(both written in Fortran) controlled by an easy-to-use Java user interface (DAJUST_UI). WhileAJUSTperforms whole-pattern matching (cell-parameter refinement, profile fitting and intensity extraction),SGAIDprovides a list of the most probable space groups. For the extraction of the integrated intensities,AJUSTuses the Le Bail procedure but with a different formula for refining the integrated intensities. Laboratory, synchrotron X-ray and neutron sources, and both reflection and transmission experimental geometries, are supported. Other program options include automated background estimation, asymmetry correction, and corrections for absorption, variable divergence and/or illumination. The extracted intensity data are written in text format and can be directly processed by the direct methods programXLENS[Rius (2011).Acta Cryst.A67, 63–67] and the multisolution direct-space structure determination programTALP[Vallcorba, Rius, Frontera & Miravitlles (2011).Acta Cryst.A67, C272].

Eurekadumpite, (Cu,Zn)16(TeO3)2(AsO4)3Cl(OH)18·7H2O, a new supergene mineral species

A new mineral eurekadumpite found at the Centennial Eureka Mine in the Tintic district of Juab County in Utah in the United States occurs in the oxidation zone along with quartz, macalpineite, malachite, Zn-bearing olivenite, goethite, and Mn oxides. Eurekadumpite forms spherulites or rosettes up to 1 mm in size and their clusters and crusts up to 1.5 cm2 in cavities. Its individuals are divergent and extremely thin (up to 0.5 mm across and less than 1 μm thick) hexagonal or roundish leaflets. The mineral is deep blue-green or turquoise-colored. Its streaks are light turquoise-colored. Its luster is satiny in aggregates and pearly on individual flakes. Its cleavage is (010) perfect and micalike. Its flakes are flexible but inelastic. Its Mohs hardness is 2.5–3.0, and D(meas) = 3.76(2) and D(calc) = 3.826 g/cm3. The mineral is optically biaxial negative, and α = 1.69(1), β ∼ γ = 1.775(5), and 2Vmeas = 10(5)°. Its pleochroism is strong: Y = Z = deep blue-green, and X = light turquoise-colored. Its orientation is X = b. The wavenumbers of the bands in the IR spectrum (cm−1; the strong lines are underlined, and w denotes the weak bands) are 3400, 2990, 1980w, 1628, 1373w, 1077, 1010, 860, 825, 803, 721w, 668, 622, 528, 461. The IR spectrum shows the occurrence of the tellurite (Te4+,O3)2− and arsenate (As5+,O4)3− anionic groups and H2O molecules; Cu and Zn cations are combined with OH− groups. The chemical composition of eurekadumpite is as follows (wt %, average of 14 electron-microprobe analyses; H2O determined using the Alimarin method): 0.04 FeO, 36.07 CuO, 20.92 ZnO, 14.02 TeO2, 14.97 As2O5, 1.45 Cl, 13.1 H2O, O = Cl2 −0.33, total 100.24. The empirical formula based on 2 Te atoms is (Cu10.32Zn5.85Fe0.01)Σ16.18(TeO3)2(AsO4)2.97[Cl0.93(OH)0.07]Σ1(OH)18.45 · 7.29H2O. The idealized formula is (Cu,Zn)16(TeO3)2(AsO4)3Cl(OH)18 · 7H2O. Eurekadumpite is monoclinic (pseudohexagonal), and the most probable space groups are P2/m, P2, or Pm. The unit-cell parameters refined from the powder X-ray data are as follows: a = 8.28(3), b = 18.97(2), c = 7.38(2) A, β = 121.3(6)°, V = 990(6) A3, and Z = 1. The strongest reflections of the X-ray powder pattern (d, A (I) [hkl]) are as follows: 18.92(100) [010], 9.45(19) [020], 4.111(13) [\(\bar 2\) 01], 3.777(24) [050, \(\bar 2\) 21, 041], 2.692(15) [\(\bar 3\) 11, 151, \(\bar 3\) 02], 2.524(41)[170, \(\bar 2\) 52, \(\bar 1\) 71], 1.558(22) [\(\bar 4\) 82, \(\bar 3\) .10.1, 024]. The name of the mineral means, firstly, that it was found in specimens from dumps of the Centennial Eureka Mine. In addition, it could mean found in a dump (the Greek word eureka means I have found it). There is an allusion to the great role that dumps of abandoned mines have played in the discovery of new minerals. Type specimens are deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences in Moscow, at the Smithsonian National Museum of Natural History in Washington, and at the American Museum of Natural History in New York.

Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal

Icosahedrite, ideally Al63Cu24Fe13, is a new mineral from the Khatyrka River, southeastern Chukhotka, Russia. It occurs as dark gray-black anhedral to subhedral grains up to 100 µm across, closely associated with spinel, diopside, forsterite, nepheline, sodalite, corundum, stishovite, khatyrkite, cupalite, and an unnamed phase of composition AlCuFe. Icosahedrite is opaque with a metallic luster, possesses a gray streak, and is brittle with an uneven fracture. The density could not be determined. For quasicrystals, by definition, the structure is not reducible to a single three-dimensional unit cell, so neither cell parameters nor Z can be given. In plane-polarized incident light, icosahedrite exhibits neither bireflectance nor pleochroism. Between crossed polars, it is isotropic. Reflectance percentages (Rmin = Rmax) for the four standard COM wavelengths are 62.3 (471.1 nm), 60.6 (548.3 nm), 58.1 (586.6 nm), and 56.0 (652.3 nm), respectively. The X-ray powder pattern was indexed on the basis of six integer indices, as conventionally used with quasicrystals, where the lattice parameter (in six-dimensional notation) is measured to be a6D = 12.64 A, with probable space group Fm3 5. The four strongest X-ray powder-diffraction lines [d in A (I/I0) (n1,n2,n3,n4,n5,n6)] are: 2.006 (100) (420 042), 2.108 (90) (422 222), 1.238 (30) (604 064), and 3.41 (25) (311 111). Average results of 34 electron-microprobe analyses gave, on the basis of total atoms = 100, the formula Al63.11Cu24.02Fe12.78Si0.03Co0.01Ca0.01Zn0.01Cr0.02Cl0.01. The simplified formula is Al63Cu24Fe13, which requires the mass fractions Al 43.02, Cu 38.60, Fe 18.38, total 100.00 wt%. The new mineral is named for the icosahedral symmetry of its internal atomic structure, as observed in its diffraction pattern. Both the new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2010-042).

Spectroscopic and structural study of the ambazone hydrochloride

Abstract Ambazone, a well-known antimicrobial compound, presents also oncostatic properties. The solid form, obtained by using solvent-drop grinding procedure, was characterized by using several physical techniques such as FTIR, X-ray photoelectron spectroscopy, 13C NMR and 15N NMR spectroscopies, thermal analysis, X-ray powder diffraction and mass spectrometry. Based on these data, it was demonstrated that an ambazone–hydrochloride was obtained: new vibrations corresponding to NH2+ were identified. DTA–TG–DSC and MS data revealed that a new crystal type has been obtained. X-ray diffraction data allowed the determination of the lattice parameters and the most probable space group P21/c was established also with only one molecule per asymmetric unit.

Time Resolved in Situ XAFS Study of the Electrochemical Oxygen Intercalation in SrFeO2.5 Brownmillerite Structure: Comparison with the Homologous SrCoO2.5 System

Low temperature oxygen ionic conductors are key materials for the development of the next generation solid oxide fuel cells. In this regard, SrMO2.5 (M = Fe,Co) systems with a Brownmillerite-type structure are able to reversibly intercalate oxygen in an electrochemical reaction at room temperature to reach SrMO3 stoichiometry. To understand and characterize this behavior, at the atomic level, in situ X-ray absorption spectroscopy experiments during the electrochemical oxidation reaction were performed for both SrFeO2.5 and SrCoO2.5 compounds at the Fe and Co K-edge, respectively. The comparative analysis of the two experiments allowed us to emphasize the similarities and differences observed during electrochemical oxidation of the two parent compounds. The data were analyzed both in XANES and EXAFS regions to extract both electronic configuration and local order information. To extract as much information as possible from collected data, the standard linear combination of spectra was complemented by the principal component analysis advanced method, which allowed us to clarify some aspects of the reaction process that were otherwise hidden. As for SrCoO2.5+x ordered intermediates (x = 0.25, 0.375) that could have been identified by neutron diffraction and XAFS experiments [J. Am. Chem. Soc. 2006, 128, 13161], no ordered intermediates of the homologous SrFeO2.5+x different from an oxygen deficient perovskite phase have been reported to occur during the oxygen intercalation reaction, except on a very local level. However, a detailed fit of the EXAFS signals for starting and final phases showed that the final fully oxidized compound (with stoichiometry SrCoO3) has been obtained for SrCoO2.5, whereas for SrFeO2.5, the reaction ended before the expected charge transfer. We interpret the formation of SrFeO3 to be accompanied by the parasitic formation of an unknown phase, containing Fe(III). Furthermore we were able to highlight that, at a local level, the most probable space group for SrCoO2.5 at ambient temperature is Imma, as the average local environments extracted from Pnma and I2mb models were not able to reproduce the experimental EXAFS spectrum.

Dalnegroite, Tl5–xPb2x(As,Sb)2l–xS34, a new thallium sulphosalt from Lengenbach quarry, Binntal, Switzerland

AbstractDalnegroite, ideally Tl4Pb2(As12Sb8)Σ20S34, is a new mineral from Lengenbach, Binntal, Switzerland. It occurs as anhedral to subhedral grains up to 200 μm across, closely associated with realgar, pyrite, Sb-rich seligmanite in a gangue of dolomite. Dalnegroite is opaque with a submetallic lustre and shows a brownish-red streak. It is brittle; the Vickers hardness (VHN25) is 87 kg mm-2 (range: 69—101) (Mohs hardness ∼3—3½). In reflected light, dalnegroite is highly bireflectant and weakly pleochroic, from white to a slightly greenish-grey. In cross-polarized light, it is highly anisotropic with bluish to green rotation tints and red internal reflections.According to chemical and X-ray diffraction data, dalnegroite appears to be isotypic with chabournéite, Tl5-xPb2x(Sb,As)21-xS34. It is triclinic, probable space group P1, with a = 16.217(7) Å, b = 42.544(9) Å, c = 8.557(4) Å, α = 95.72(4)°, β = 90.25(4)°, γ = 96.78(4)°, V = 5832(4) Å3, Z = 4.The nine strongest powder-diffraction lines [d(Å) (I/I0) (hkl)] are: 3.927 (100) ( 10 0); 3.775 (45) (22); 3.685 (45) (60); 3.620 (50) (440); 3.124 (50) (2); 2.929 (60) (42); 2.850 (70) (42); 2.579 (45) (0 2); 2.097 (60) (024). The mean of 11 electron microprobe analyses gave elemental concentrations as follows: Pb 10.09(1) wt.%, Tl 20.36(1), Sb 23.95(1), As 21.33(8), S 26.16(8), totalling 101.95 wt.%, corresponding to Tl4.15Pb2.03(As11.86Sb8.20)S34. The new mineral is named for Alberto Dal Negro, Professor in Mineralogy and Crystallography at the University of Padova since 1976.

Scandium tungstate above 2.5 GPa

Synchrotron x-ray powder diffraction was used to study Sc 2W 3O 12 in a diamond anvil cell up to 6.2 GPa in order to better characterize the second high pressure phase observed in earlier in-situ diffraction studies. Two crystalline-to-crystalline phase transitions were observed, in line with the earlier work. Above 2.7 GPa, Sc 2W 3O 12 adopted a monoclinic structure with probable space group P2 1/n, that is distinct from the monoclinic phase existing between 0.3 GPa and 2.7 GPa. The bulk modulous ( K 0 ) for this second high pressure phase was estimated to be 90(3) GPa using a Birch–Murnaghan equation of state with K p fixed at 4. Refining K p resulted in K 0 = 72 ( 3 ) GPa and K p = 12 ( 1 ) . The transition at ∼2.7 GPa on compression involved a unit cell volume reduction of almost 18% and was not reversible on decompression to atmospheric pressure at ambient temperature, suggesting that changes in bonding occur at the phase transition. Linear compressibility values for this high pressure monoclinic phase were estimated to be β a = 3.6 ( 1 ) × 1 0 − 3 GPa − 1 , β b = 3.7 ( 2 ) × 1 0 − 3 GPa − 1 , β c = 2.0 ( 1 ) × 1 0 − 3 GPa − 1 by straight line fits to the lattice constants over the range 0–6.2 GPa.

Crystal structure of pollucite

Abstract The crystal structure of pollucite (ANA) (Cs,Na)AlSi2O6 is characterized by single-crystal X-ray diffractometry. The space group C2/c, monoclinic, is found to be the most probable space group for this mineral based on the systematic absences of reflections. Cesium ions or water molecules are disordered at the center of a channel and are slightly apart from the special position. This is the origin of symmetry breaking and the space group becomes lower from Ia-3d (analcime) to C2/c. Sodium ions or vacancies are located at the contact point of the channel. No ordering of aluminum is observed in the pollucite structure.