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Owyheeite [Cu0.09 (1)Ag2.77 (4)Pb10.23 (4)Sb10.89 (5)S28.00 (5)] crystallizes as a twofold superstructure with P21/n symmetry and pseudo‐orthorhombic metrics [a = 8.1882 (3) Å, b = 27.2641 (7) Å, c = 22.8679 (7) Å, β = 90.293 (3)°, V = 5105.0 (3) Å3, Z = 4]. Owyheeite is systematically twinned by reflection at (021) or equivalently (021). Twinning is explained by describing a simplified Pmcn archetype structure as polytype built of two kinds of rods, which contact via electron‐pair micelles. A procedure of generating hypothetical polytypes by tiling space with partially overlapping equivalent regions is described. [ABSTRACT FROM AUTHOR]

Prachařite, ideally CaSb5+2(As3+2O5)2O2·10H2O, is a new mineral found in underground workings of the Plaka Mine No. 80, Plaka, Lavrion Mining District, Attica, Greece. It occurs as colourless to white, thin tabular hexagonal, in general sharp crystals up to 2.5 mm in diameter, and is associated with pharmacolite, sulphur and very rare smamite {Ca2Sb(OH)4[H(AsO4)2]·6H2O} on a matrix composed of sphalerite, galena and carbonate gangue. Prachařite is translucent to transparent, with a glassy lustre, white streak, a good cleavage parallel to {0001} and a distinct cleavage parallel to {10 1 ¯ 0}. It is non-luminescent, brittle, and has an uneven fracture, a Mohs hardness of 2–2.5 and X-ray density Dx = 2.848 g/cm3, Dcalc. = 2.836–2.853 g/cm3 (for two measured compositions). Optically, it is uniaxial negative, with ω = 1.619(1) and ε = 1.553(1). Prachařite is trigonal, space group P 3 ¯ c1 (no. 165), with a = 13.951(2), c = 19.899(2) Å, V = 3354.1(10) Å3 and Z = 6. Strongest lines in the X-ray powder diffraction pattern are [d in Å (I) hkl]: 9.894 (100) 002; 6.045 (8) 200; 5.156 (10) 202; 4.946 (11) 004; 3.297 (19) 311, 006, 222; 2.988 (22) 400, 313, 116. Two sets of independent electron probe micro-analyses yielded (wt%): CaO 6.28/7.12, MgO 0.09/-, Zn -/0.01, Sb2O5 39.22/40.19, As2O3 47.59/47.39, SO3 -/0.02, H2O 21.65/22.04 (calculated on the basis of ideal composition derived from crystal-structure determination), total 114.83/116.77; the total is reproducibly high due to a loss of a third of all water molecules under the electron beam. The empirical formulae, based on O = 22 atoms per formula unit, for the two datasets are very similar, (Ca0.93Mg0.02)Σ0.95Sb2.02(AsO3)4.00·10H2O and Ca1.04Sb2.03(AsO3)3.92·10H2O. The ideal formula is CaSb5+2(As3+2O5)2O2·10H2O, determined with the help of a crystal-structure determination based on single-crystal X-ray diffraction datasets collected at room temperature (R1 = 2.3%). The atomic arrangement of prachařite is unusual; it is based on two different layers containing a six-membered ring of corner-sharing SbO6 octahedra, an eight-coordinated Ca1 atom in the centre of the ring, two non-equivalent AsO3 groups corner-linked to form a (As2O5)4− diarsenite group, and, on interlayer sites, a seven-coordination Ca2 atom and three water molecules (all only weakly hydrogen-bonded), one of which is only partially occupied (split position). The mineral is named in honour of Dr Ivan Prachař, a long-term researcher of the mineralogy and underground workings of Lavrion. [ABSTRACT FROM AUTHOR]

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The Tissint meteorite fell on July 18, 2011 in Morocco and was quickly recovered, allowing the investigation of a new unaltered sample from Mars. We report new high‐field strength and highly siderophile element (HSE) data, Sr‐Nd‐Hf‐W‐Os isotope analyses, and data for cosmogenic nuclides in order to examine the history of the Tissint meteorite, from its source composition and crystallization to its irradiation history. We present high‐field strength element compositions that are typical for depleted Martian basalts (0.174 ppm Nb, 17.4 ppm Zr, 0.7352 ppm Hf, and 0.0444 ppm W), and, together with an extended literature data set for shergottites, help to reevaluate Mars' tectonic evolution in comparison to that of the early Earth. HSE contents (0.07 ppb Re, 0.92 ppb Os, 2.55 ppb Ir, and 7.87 ppb Pt) vary significantly in comparison to literature data, reflecting significant sample inhomogeneity. Isotope data for Os and W (187Os/188Os = 0.1289 ± 15 and an ε182W = +1.41 ± 0.46) are both indistinguishable from literature data. An internal Lu‐Hf isochron for Tissint defines a crystallization age of 665 ± 74 Ma. Considering only Sm‐Nd and Lu‐Hf chronometry, we obtain, using our and literature values, a best estimate for the age of Tissint of 582 ± 18 Ma (MSWD = 3.2). Cosmogenic radionuclides analyzed in the Tissint meteorite are typical for a recent fall. Tissint's pre‐atmospheric radius was estimated to be 22 ± 2 cm, resulting in an estimated total mass of 130 ± 40 kg. Our cosmic‐ray exposure age of 0.9 ± 0.2 Ma is consistent with earlier estimations and exposure ages for other shergottites in general. [ABSTRACT FROM AUTHOR]

Agmantinite, ideally Ag2MnSnS4, is a new mineral from the Uchucchacua polymetallic deposit, Oyon district, Catajambo, Lima Department, Peru. It occurs as orange–red crystals up to 100 μm across. Agmantinite is translucent with adamantine lustre and possesses a red streak. It is brittle. Neither fracture nor cleavage were observed. Based on the empirical formula the calculated density is 4.574 g/cm3. On the basis of chemically similar compounds the Mohs hardness is estimated at between 2 to 2½. In plane-polarised light agmantinite is white with red internal reflections. It is weakly bireflectant with no observable pleochroism with red internal reflections. Between crossed polars, agmantinite is weakly anisotropic with reddish brown to greenish grey rotation tints. The reflectances (R min and R max) for the four standard wavelengths are: 19.7 and 22.0 (470 nm); 20.5 and 23.2 (546 nm); 21.7 and 2.49 (589 nm); and 20.6 and 23.6 (650 nm), respectively. Agmantinite is orthorhombic, space group P 21 nm , with unit-cell parameters: a = 6.632(2), b = 6.922(2), c = 8.156(2) Å, V = 374.41(17) Å3, a : b : c 0.958:1:1.178 and Z = 2. The crystal structure was refined to R = 0.0575 for 519 reflections with I > 2σ(I). Agmantinite is the first known mineral of ${M}_{\rm 2}^{\rm I} $ M II M IVS4 type that is derived from wurtzite rather than sphalerite by ordered substitution of Zn, analogous to the substitution pattern for deriving stannite from sphalerite. The six strongest X-ray powder-diffraction lines derived from single-crystal X-ray diffraction data [ d in Å (intensity)] are: 3.51 (s), 3.32 (w), 3.11 (vs), 2.42 (w), 2.04 (m) and 1.88 (m). The empirical formula (based on 8 apfu) is (Ag1.94Cu0.03)Σ1.97(Mn0.98Zn0.05)Σ1.03Sn0.97S4.03.The crystal structure-derived formula is Ag2(Mn0.69Zn0.31)Σ1.00SnS4 and the simplified formula is Ag2MnSnS4. The name is for the composition and the new mineral and mineral name have been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA2014-083). [ABSTRACT FROM AUTHOR]

The Pb-Ag-Sb sulfide roshchinite, Cu0.09Ag1.04Pb 0.65Sb2.82As0.37S6.08, is a lillianite homologue N = 4 with a complex incommensurate superstructure in the 8.46 Å direction of the orthorhombic crystal lattice with a 19.0804(1) Å, b 8.4591(2) Å and c 12.9451(3) Å, superspace group Pbcn(0s20)00s, q = 0.41458(3)b*. A structure solution and refinement in (3+1) superspace, based on 10,019 observed reflections and 437 refined parameters was terminated at Robs (wR) equal to 7.27 (8.07)% using satellites up to second order; Robs is 4.82 for main reflections only. The Pb atoms in trigonal coordination prisms on planes of unitcell twinning are semiperiodically replaced by antimony. The marginal columns of (311)PbS slabs of the Sb-Ag based structure which is based on PbS-like topology contain Sb, Ag(Cu) and mixed Ag/Sb sites in a complicated sequence. Central portions of the slabs are occupied by Sb-S crankshaft chains, best exposed on the (100)PbS planes, which run diagonally across the slabs. In these planes, in their majority the chains display Sb3S4 form and two opposing orientations, zig-zagging along the [010] direction. Every six chains, a parallel configuration of two chains occurs, but occasionally this interval is reduced to five chains. This, together with related compositional changes in the Pb- and Ag-Sb column, explains the one-dimensionally incommensurate character of roshchinite. Modestly elevated contents of As replacing Sb are the probable reason of modulation and non-commensurability in roshchinite. [ABSTRACT FROM AUTHOR]

Polloneite, ideally AgPb46As26Sb23S120, is a new N=4 member of the sartorite homologous series. It occurs in a matrix of baryte from the Pizzone level of the Pollone baryte-pyrite-(Pb-Zn-Ag) deposit at Valdicastello Carducci, near Pietrasanta, in the Apuan Alps, Tuscany, Italy, as anhedral grains up to 0.5mm across. The mineral is opaque, greyish black with a metallic lustre. In reflected light polloneite is white, bireflectance is moderate. Internal reflections are absent. Under crossed polars, anisotropism is moderate with rotation tints in brown-violet and deep grey. The reflectance data (%, air) are: 30.2, 42.4 at 470nm, 28.8, 41.0 at 546nm, 27.9, 39.8 at 589nm and 26.0, 37.4 at 650nm. Mohs hardness is 3-3½, microhardness VHN50 exhibits a mean value of 200kg mm-2. The average results of 15 electron-microprobe analyses of three grains are Ag 0.71(5), Pb 52.05(21), As 10.61(22), Sb 15.40(12), S 21.16(8), total 99.92(15) wt.%, corresponding to Ag1.20Pb45.76As25.79Sb23.04S120.21 (on the basis of Me+S=216 apfu). The simplified formula AgPb46As26Sb23S120 is in accordance with the results of a crystal structure determination. The calculated density is 5.77g cm-3. Polloneite is monoclinic, space group P21, a=8.413(2), b=25.901(5), c=23.818(5) Å, β=90.01(3)°, V=5189.8(18) ų, Z=1. The strongest eight lines in the calculated powder-diffraction pattern [d in Å(I)hkl] are 3.795(100)(026), 3.414(60)(233), 3.238(69)(080), 3.020(97)(253), 2.922(82)(066), 2.738(73)(236), 2.375(79)(290) and 2.103(64)(400). Polloneite is a new N=4 member of the sartorite homologous series with substantial Sb and small, but important, Ag content. It is a three-fold superstructure with a tripled unit-cell parameter, 7.9 Å, of sartorite homologues. In the As-Sb rich slabs, several types of crankshaft chains and isolated (As,Sb)-S polyhedra occur. A sequence of three different, tightly bonded double-layer fragments (broad ribbons) contains two asymmetric fragments with long crankshaft chains whereas the third fragment type, with Ag, contains small mirror-symmetrical metalloid groups and no crankshaft chains. This configuration can potentially cause order-disorder phenomena in the structure. The threefold superstructure and the mixed As-Sb character distinguish polloneite from veenite and from dufrénoysite, respectively. [ABSTRACT FROM AUTHOR]

The crystal structure of veenite is reported for the first time from a sample from the type locality of Madoc (Ontario, Canada). It has been solved and refined by X-ray single-crystal diffraction on the basis of 4973 observed reflections (with Fo > 4σ(Fo)) with a final R1 = 0.0396. Veenite is monoclinic P21, with unit-cell parameters a = 8.429(2), b = 26.069(5), c = 8.962(2) Å, β = 117.447(2)°. The bulk veenite composition is Ag0.15Pb16.029Sb8.836As6.99S39.95 (for Z = 1) corresponding to N = 4.09 (Me8NS8N+8, theoretical value is 4.0), with the percentage of the Ag-(As,Sb) substituted end-member only equal to 3.51 mol.%, i.e., a nearly pure Pb-Sb-As sulfosalt. The crystal structure is typical for the N = 4 sartorite homologue, with zig-zag walls of trigonal coordination prisms of Pb which separate slabs of diagonally oriented double-layers populated by Sb and As with partial Pb substitution. Orientation of three-membered crankshaft chains formed by strong (As,Sb) - S bonds on the two surfaces of double-layers differs substantially from that in dufrénoysite, which is a pure Pb-As (N = 4) sulfosalt. [ABSTRACT FROM AUTHOR]

The crystal structure of argentobaumhauerite is reported for the first time from a sulfosalt aggregate from Lengenbach deposit, Binntal, Switzerland. The chemical formula of argentobaumhauerite, calculated in agreement with the results of structure determination is Cu0.06Ag1.20Tl0.18Pb21.46Sb0.56As32.28S72.26. The difference from the idealized baumahuerite formula, Pb12As16S36, and from the formula of Ag-, Tl- and Sb-free baumhauerite from Moosegg, Austria, Pb11.80As16.28S35.92, expresses the Ag + As and Tl + As substitution for 2Pb. Argentobaumhauerite is triclinic, a = 7.9053(10), b = 8.4680(10), c = 44.4102(53) Å, α = 84.614(2), β = 86.469(2), γ = 89.810(2)°. V(cell) = 2954.16 ų, space group PEmbedded Image. Baumhauerite Pb11.80As16.28S35.92 from Moosegg is triclinic, a = 7.884(4), b = 8.345(4), c = 22.811(11) Å, α = 90.069(8), β = 97.255(8), γ = 90.082(8)°, V(cell) = 1488.8(13) Å3, space group P1. Both minerals represent the N1,2 = 3;4 = 3.5 member of the sartorite homologous series, with As-rich slabs separated by zigzag layers of trigonal coordination prisms of lead. In argentobaumhauerite the sequence of alternating N = 3 and N = 4 slabs of baumhauerite is further modified by alternation of two distinct types of N = 4 slabs, those with Pb present in the slab interior and those with the interior Pb substituted by Ag + As. The length and arrangement of crankshaft chains of short As-S bonds differs between different slabs, and especially between the N = 4 slabs of baumhauerite and argentobaumhauerite. The name 'argentobaumhauerite' replaces the preliminary name 'baumhauerite-2a' (IMA-CNMNC; accepted proposal 15-F). [ABSTRACT FROM AUTHOR]

Oscarkempffite, ideally Ag10Pb4(Sb17Bi9)Σ=26S48, is a new mineral species found in old material (1929-30) from the Colorada vein, Animas mine, Chocaya Province, Department of Potosi, Bolivia. It is associated with aramayoite, stannite, miargyrite, pyrargyrite and tetrahedrite. Oscarkempffite forms anhedral grains and grain aggregates up to 10 mm across. The mineral is opaque, greyish black with a metallic lustre; it is brittle without any discernible cleavage. In reflected light oscarkempffite is greyish white, pleochroism is distinct, white to dark grey. Internal reflections are absent. In crossed polars, anisotropism is distinct with rotation tints in shades of grey. The reflectance data (%, air) are: 39.9, 42.6 at 470 nm, 38.6, 41.7 at 546 nm, 38.1, 41.2 at 589 nm and 37.3, 40.6 at 650 nm. Mohs hardness is 3-3½, microhardness VHN50 exhibits a range 189-208, with a mean value 200 kg mm−2. The average results of four electron-microprobe analyses in a grain are: Cu 0.24(7), Ag 14.50(8), Pb 11.16(14), Sb 28.72(16), Bi 24.56(17), S 20.87(5), total 100.05(6) wt.%, corresponding to Cu0.24Ag9.92Pb4.00Sb17.36Bi8.64S47.84 (on the basis of Me+S=88 apfu). The simplified formula, Ag10Pb4Sb17Bi9S48, is in accordance with the results of a crystal-structure determination. The density, 5.8 g cm-3, was calculated using the ideal formula. Oscarkempffite has an orthorhombic cell with a=13.199(2), b=19.332(3), c=8.249(1) Å, V=2116.3(5) ų, space group Pnca and Z=1. The strongest eight lines in the (calculated) powder-diffraction pattern are [d in Å(I)hkl]: 3.66(35)(122), 3.37(70)(132), 3.34(100)(250), 2.982(55)(312), 2.881(86)(322), 2.733(29)(332), 2.073(27)(004) and 2.062(31)(182). Comparison with gustavite, andorite and roshchinite confirms its independence as a mineral species. [ABSTRACT FROM AUTHOR]

The members of the sartorite homologous series are complex sulfides Me2+8N - 16 - 2XMe3+16+XMe+XS8N+8 where Me2+ is Pb and Me3+ is As and Sb, whereas Me+ is Ag and/or Tl. This paper presents calculation formulae for the homologue order N and for the separate substitution percentages for Tl + (As,Sb) ↔ 2Pb and Ag + (As,Sb) ↔ 2Pb substitutions. This enables one to evaluate the crystal chemistry and build a systematic classification of the sartorite homologues. [ABSTRACT FROM AUTHOR]

On February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long-lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of 14C, 22Na, 26Al, 54Mn, 57Co, 58Co, and 60Co, which indicate that the pre-atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed 26Al activities of the investigated samples, Monte Carlo simulations, and taking into account the 26Al half-life (0.717 Myr), the cosmic-ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, 14C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of 14C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic 137Cs and primordial 40K in some of the Chelyabinsk fragments. [ABSTRACT FROM AUTHOR]

Ferdowsiite is monoclinic, a=8.677(2) Å, b=5.799(1) Å, c=13.839(3) Å, β=96.175(4)°, unit cell volume 692.3 Å3. Space group P21/ n. Refinement from single-crystal X-ray diffraction data reached R1=0.028 for 626 Fo>4σ( Fo) and 0.032 for all 716 Fo used. Value of wR2 is 0.065. The crystal structure of ferdowsiite, approximately Ag8Sb4(As,Sb)4S16, contains four distinct cation and four different anion sites in the asymmetric unit, all in general positions. Besides two Ag sites and one Sb site, the crystal structure contains one mixed As-Sb coordination polyhedron (0.63 As and 0.37 Sb in the site). The Sb1 site has three short Sb-S bonds 2.503-2.645 Å. As and Sb in the mixed site were refined separately, with isotropic displacement coefficients. As has typical bond length values of 2.248-2.354 Å whereas Sb has 2.443-2.392 Å, i.e., the observed ligand positions are visibly influenced by the predominant arsenic. The crystal structure of ferdowsiite is a superstructure of a PbS like motif. The {100} planes of the PbS-like substructure are the (105̅), (301) and (010) planes in terms of the ferdowsiite lattice. The structure contains zig-zag chains of Sb1 connected via short Sb-S bonds and flanked by (Sb,As)S3 groups and Ag polyhedra. Groups of four SbS5-and (Sb,As)S5 coordination pyramids form an interconnected network with interspaces which accommodate both the lone electron pairs and the tetrahedrally coordinated Ag situated in coordination octahedra. Partial lead substitution takes place in the coordination polyhedra of Sb1 and Ag2. In the paper, the structure is compared with the other Ag(As,Sb,Bi)(S,Se)2 structures. The configurationally closest PbS-based homeotypic structure, however, is diaphorite, which is an ordered superstructure of the ferdowsiite arrangement, with a substantial presence of Pb, and without As. [ABSTRACT FROM AUTHOR]

Exact, contact-free and non-destructive optical analysis of semiconducting layers is advantageous for thin-film solar cell applications. A non-numerical theoretical model has been developed to extract approximation-free optical and electrical data from UV/visible (Vis)/near infra-red (NIR) spectra. Special focus has been set on single-layer systems. Approximations for thin-films upon substrates and measurements without integrating sphere are provided. Complex parameter evaluation is provided. This exact data acquisition model provides deeper insight into the process-parameter dependencies of pulsed direct current sputtered, transparent aluminum doped zinc-oxide (ZnO:Al) thin films, upon glass substrates. ZnO:Al thin films have been analyzed with respect to space-time dependencies of the sputter process. Therefore, sputter-depositions have been examined, referring to positions upon the substrate, r, target-substrate distances, dTarSub, and sputter durations, tSp. Results were compared with those of the well-known Keradec/Swanepoel model. The necessity of taking both spectra—transmission and reflection spectra—into account has been shown. Theoretical sputter-concepts were proved and enhanced. A non-contact, optical conductivity measurement possibility by use of UV/Vis/NIR spectroscopy has been provided. Optically evaluated conductivities, \sigmaL, were compared with electrically taken values, by a four-tip measurement system. [ABSTRACT FROM AUTHOR]

Presents information on a study which discussed the ninefold superstructure of sartorite crystal. Sample description; Experimental procedures; Discussion of the ninefold superstructure of sartorite; Coordination polyhedra.

Presents a study which focused on the mineralogical description of baumstarkite and its chemical separation with respect to aramayoite and miargyrite. Occurrence and physical properties; Chemical composition; Results of electron-microprobe investigations.

Crystal-structure refinements in space group P21/c were performed on five grains of rathite with different types and degrees of thallium, silver, and antimony substitutions, as well as quantitative electron-microprobe analyses of more than 800 different rathite samples. The results of these studies both enlarged and clarified the complex spectrum of cation substitutions and the crystal chemistry of rathite. The [Tl+ + As3+] ↔ 2Pb2+ scheme of substitution acts at the structural sites Pb1, Pb2, and Me6, the [Ag+ + As3+] ↔ 2Pb2+ substitution at Me5, and the Sb-for-As substitution at the Me3 site only. The homogeneity range of rathite was determined to be unusually large, ranging from very Tl-poor compositions (0.16 wt%; refined single-crystal unit-cell parameters: a = 8.471(2), b = 7.926(2), c = 25.186(5) Å, β = 100.58(3)°, V = 1662.4(6) Å3) to very Tl-rich compositions (11.78 wt%; a = 8.521(2), b = 8.005(2), c = 25.031(5) Å, β = 100.56(3)°, V = 1678.4(6) Å3). The Ag content is only slightly variable (3.1 wt%–4.1 wt%) with a mean value of 3.6 wt%. The Sb content is strongly variable (0.20 wt%–7.71 wt%) and not correlated with the Tl content. With increasing Tl content (0.16 wt%–11.78 wt%), a clear increase of the unit-cell parameters a, b, and V, and a slight decrease of c is observed, although this is somewhat masked by the randomly variable Sb content. The revised general formula of rathite may be written as AgxTlyPb16−2(x+y)As16+x+y−zSbzS40 (with 1.6 < x < 2, 0 < y < 3, 0 < z < 3.5). Based on Pb–S bond lengths, polyhedral characteristics and Pb-site bond-valence sums, we conclude that the Pb1 site is more affected by Tl substitution than the Pb2 site. When Tl substitution reaches values above 13 wt% (or 3 apfu), a new phase ("SR"), belonging to the rahite group, appears as lamellar exsolution intergrowths with Tl-rich rathite (11.78 wt%). Rathite is found only in the Lengenbach and Reckibach deposits, Binntal, Canton Wallis, Switzerland. [ABSTRACT FROM AUTHOR]

The Pb-Ag-Sb sulfide roshchinite, Cu0.09Ag1.04Pb 0.65Sb2.82As0.37S6.08, is a lillianite homologue N = 4 with a complex incommensurate superstructure in the 8.46 Å direction of the orthorhombic crystal lattice with a 19.0804(1) Å, b 8.4591(2) Å and c 12.9451(3) Å, superspace group Pbcn(0s20)00s, q = 0.41458(3)b*. A structure solution and refinement in (3+1) superspace, based on 10,019 observed reflections and 437 refined parameters was terminated at Robs (wR) equal to 7.27 (8.07)% using satellites up to second order; Robs is 4.82 for main reflections only. The Pb atoms in trigonal coordination prisms on planes of unitcell twinning are semiperiodically replaced by antimony. The marginal columns of (311)PbS slabs of the Sb-Ag based structure which is based on PbS-like topology contain Sb, Ag(Cu) and mixed Ag/Sb sites in a complicated sequence. Central portions of the slabs are occupied by Sb-S crankshaft chains, best exposed on the (100)PbS planes, which run diagonally across the slabs. In these planes, in their majority the chains display Sb3S4 form and two opposing orientations, zig-zagging along the [010] direction. Every six chains, a parallel configuration of two chains occurs, but occasionally this interval is reduced to five chains. This, together with related compositional changes in the Pb- and Ag-Sb column, explains the one-dimensionally incommensurate character of roshchinite. Modestly elevated contents of As replacing Sb are the probable reason of modulation and non-commensurability in roshchinite. [ABSTRACT FROM AUTHOR]

Shape and lattice orientation relations as well as chemical compositions of Fe-Ti-oxide micro-inclusions and plagioclase host crystals in rocks of a gabbro-plagiogranite assemblage from the Mid-Atlantic ridge at 13°34' N were studied using electron back scatter diffraction, transmission electron microscopy and field-emission gun-electron microprobe analyzer. Several evolutionary stages of the micro-inclusion-host assemblages were discerned, starting with precipitation of Fe-Ti-oxides from a super-saturated plagioclase in otherwise unaltered gabbro, followed by transformation and re-crystallization of the micro-inclusions as well as chemical alteration of both inclusions and host during plagiogranite intrusion and subsequent hydrothermal alteration. A detailed sequence of petrogenetic processes could be reconstructed. Fe-Ti-oxide micro-inclusions are the main carriers of the paleo-magnetic record of these rocks, and understanding the transformations affecting Fe-Ti-oxide microinclusions in the highly dynamic mid-ocean ridge environment is crucial for interpreting paleo-magnetic data. [ABSTRACT FROM AUTHOR]

• First data on the meteorite flux to Earth during the Frasnian–Famennian bioevent. • No support of asteroid shower, but comet or carbonaceous asteroid shower cannot be ruled out. • Meteorite flux supports eccentricity minimum in Earth's orbit at bioevent. • First picture of the variations in meteorite flux through the Phanerozoic. • Ordinary chondrites made up a major fraction of the flux since at least 466 Ma ago. We have reconstructed the distribution of extraterrestrial chrome spinels in a marine limestone section across the Frasnian–Famennian stratotype section at Coumiac in southern France, providing the first insights on the types of micrometeorites and meteorites that fell on Earth at this time. The data can test whether the small cluster of roughly coeval, large impact structures is related to an asteroid breakup and shower with possible bearings also on the late Devonian biodiversity crisis. A total of ∼180 extraterrestrial spinel grains (>32 μm) were recovered from 957 kg of rock. Noble-gas measurements of individual grains show high solar-wind content, implying an origin from decomposed micrometeorites. Element analyses indicate a marked dominance of ordinary chondritic over achondritic grains, similar to the recent flux. The relation between H, L and LL meteorites is ∼29–58–13%, similar to the late Silurian flux, ∼31–63–6%, but different from the distribution, ∼45–45–10%, in the recent and the Cretaceous flux. Our data show no indication of a generally enhanced late Devonian micrometeorite flux that would accompany an asteroid shower. However, in a single limestone bed that formed immediately before the Upper Kellwasser horizon, that represents the main end-Frasnian species-turnover event, we found an enrichment of ∼10 ordinary chondritic grains (>63 μm) per 100 kg of rock, compared to the ∼1–3 grains per 100 kg that characterise background. The anomalously abundant grains are of mixed H, L and LL types and may be related to an enhanced flux of extraterrestrial dust during postulated minima in both the 405 ka and 2.4 Ma Earth-orbit eccentricity cycles at the onset of the Upper Kellwasser event. In the present solar system the dust accretion at Earth is the highest at eccentricity minima because of the spatial distribution of dust bands of the zodiacal cloud. Besides this small grain anomaly the data here and in previous studies support a stable meteorite flux through the late Silurian and Devonian, in contrast to the mid-Ordovician, when achondritic meteorites that are rare on Earth today were common, followed by the influx of a flood of debris related to the breakup of the L-chondrite parent body. Our accumulated data for six time windows through the Phanerozoic indicate that the ordinary chondrites make up a major fraction in the meteorite flux since at least the mid-Ordovician. We note that the sources in the asteroid belt of the H and L meteorites, the two most common types of meteorites today and through much of the Phanerozoic, remain elusive. [ABSTRACT FROM AUTHOR]