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ABSTRACT Lafossaite, idealized formula TlCl, is cubic, space group P-m3m (by analogy with the synthetic inorganic equivalent) with unit-cell parameter refined from powder data: a = 3.8756(3) [Angstrom], V = [...]

Synthetic nagyagite was grown from a melt as part of a search for materials with high-temperature superconductivity. Electron microprobe analyses of synthetic nagyagite and of nagyagite from the type locality Nagyag, Transylvania (now Sacarimb, Romania) agree with data from literature. The crystal chemical formula [Pb(Pb,Sb)[S.sup.2]][(Au,Te)] was derived from crystal structure investigations. Nagyagite is monoclinic pseudotetragonal. The average crystal structure was determined from both synthetic and natural samples and was refined from the synthetic material to R = 0.045 for 657 single-crystal X-ray data: space group P[2.sub.1]/m, a = 4.220(1) [Angstrom], b = 4.176(1) [Angstrom], c = 15.119(3) [Angstrom], [Beta] = 95.42(3) [degrees], and Z = 2. Nagyagite features a pronounced layer structure: slices of a two slabs thick SnS-archetype with formula Pb(Pb,Sb)[S.sub.2] parallel to (001) have a thickness of 9.15 [Angstrom]. Te and Au form a planar pseudo-square net that is sandwiched between the SnS-archetype layers; it is assumed that planar [Au.sup.[4Te]][Te.sub.4] configurations are edge connected to chains and that Te atoms are in a zigzag arrangement. Ordering within the SnS-archetype and gold-tellurium layers, intense twinning and/or stacking variants are responsible for the often observed superstructure reflections. For buckhornite, [[([Pb.sub.2]Bi).sub.[Sigma]3][S.sub.3]][[(AuT[e.sub.2]).sub.[Sigma]3]], a structure model is proposed considering a homologous series with nagyagite, [[([Pb.sub.3](Pb,Sb).sub.3])[Sigma]6][S.sub.6]][[(Au,Te).sub.3]].

The incommensurately modulated crystal structure of the mineral daliranite has been determined using 3D electron diffraction data obtained on nanocrystalline domains. Daliranite is orthorhombic with a = 21, b = 4.3, c = 9.5 Å and shows modulation satellites along c. The solution of the average structure in the Pnma space group together with energy‐dispersive X‐ray spectroscopy data obtained on the same domains indicate a chemical formula of PbHgAs2S5, which has one S fewer than previously reported. The crystal structure of daliranite is built from columns of face‐sharing PbS8 bicapped trigonal prisms laterally connected by [2+4]Hg polyhedra and (As3+2S5)4− groups. The excellent quality of the electron diffraction data allows a structural model to be built for the modulated structure in superspace, which shows that the modulation is due to an alternated occupancy of a split As site. [ABSTRACT FROM AUTHOR]

Suredaite, ideally PbSn[S.sub.3], is a new mineral species from the Pirquitas Ag-Sn deposit (Province Jujuy, NW-Argentina). It was observed in symmetrically banded veins in the Oploca district, and is associated with sphalerite, arsenopyrite, pyrite-marcasite, cassiterite, cylindrite, franckeite, hocartite, rhodostannite, and various Ag-Sb and Ag-Bi sulfosalts in minor amounts. Suredaite occurs in layers up to 1 cm in thickness as aggregates of radially arranged tabular-prismatic (single) crystals, has a metallic lustre, and a dark grey streak. [VHN.sub.50] ranges between 18.2 and 20.6 (mean 19.6) GPa, the Mohs hardness is 2.5-3. It has perfect cleavages parallel to {001}, {101}, and {100}. The measured density varies between 5.54 and 5.88 g/[cm.sup.3], [D.sub.x] was determined to be 5.615 g/[cm.sup.3]. In reflected plane-polarised light, it is white and is not perceptibly bireflectant or pleochroic. It lacks internal reflections and is weakly anisotropic with metallic blue, mauve to brown rotation tints. Specular reflectance percentages in air and in oil are tabulated from 400 to 700 nm and compared graphically with those for the type specimen of teallite, PbSn[S.sub.2]. Electron microprobe analyses showed suredaite to be chemically inhomogeneous with respect to the compositional variations (in wt%): Pb 42.3-48.5, Ag 0.3-1.1, Fe 0.3-1.0, As 0.2-2.1, Sn 27.7-30.2, S 23.1-24.7. The crystal structure determined from single-crystal X-ray diffraction data revealed orthorhombic symmetry [space group Pnma, Z = 4, a = 8.8221 (3), b = 3.7728(3), c = 14.0076(3) [Angstrom]; V = 466.23(4) [[Angstrom].sup.3]. The atomic arrangement is isostructural to the [NH.sub.4]Cd[Cl.sub.3] structure type which exists in a series of isotypic sulfides and selenide compounds. The suredaite structure, which is the natural analogue of synthetic PbSn[S.sub.3], consists of columns of double-edge sharing octahedra running parallel to the b axis, which house the Sn atoms. These columns are linked by rods of eightfold-coordinated Pb atoms. On the basis of the structure determination, the empirically determined idealized formula follows a [sup.[8]](Pb, As,Ag, Sn) [sup.[6]](Sn,Fe)[S.sub.3] stoichiometry. Crystalchemical arguments suggest Ag possibly to occupy interstitial sites according to the alternative formula [sup.[14]]([],Ag) [sup.[8]](Pb, As, Sn) [sup.[6]](Sn,Fe) [S.sub.3]. The name of this new mineral species is in honor of R.J. Sureda Leston, head of the Department of Mineralogy and Economic Geology, University of Salta, Argentina.

The crystal structure of the mineral gortdrumite, a rare copper-mercury-iron sulfide, was solved using intensity data collected using a crystal from the Neuschurf adit, Leogang, Salzburg, Austria. This study revealed that the structure is triclinic, space group P $\bar 1$ , with cell parameters: a = 9.677(4), b = 9.865(5), c = 11.992(5) Å, α = 77.85(4), β = 79.42(3), γ = 76.30(4)°, V = 1076.5(8) Å3 and Z = 1. The refinement led to an R index of 0.0833 for 3335 independent reflections and 143 parameters. Twelve S sites (one with half occupancy) and eighteen metal sites (5 Hg, 12 Cu and 1 Fe) occur in the crystal structure of gortdrumite. Mercury cations link two sulfur atoms in a linear coordination, Cu cations are found in various low-coordination (2, 3 and 4) sites, in agreement with the Cu preference for such environments, and Fe in tetrahedral coordination. Metal–metal interactions are also present and these contacts are discussed in relation with other copper sulfides, intermetallics and pure metals. Electron microprobe analyses of the crystal used for the structural study led to the formula Cu24.83Fe1.73Hg9.09S22.35, on the basis of 58 atoms. On the basis of information gained from the structural and chemical characterization, the crystal-chemical formula was revised to Cu24Fe2Hg9S23 (Z = 1) instead of (Cu,Fe)6Hg2S5 as reported previously. [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 crystal structure of braithwaiteite, NaCu2+5(Sb5+Ti4+)O2(AsO4)4(AsO3OH)2(H2O)8, triclinic, Z=1, P1, a=7.0308(4), b=9.8823(5), c=10.6754(6)Å, α=106.973(1), β=104.274(1), γ=93.839(1)°, V=679.76(11)Å3, was solved by direct methods and refined to an R1 index of 0.025 for 3584 observed reflections. A prominent motif in the braithwaiteite structure is a chain of corner-sharing (Sb,TiO6) octahedra that is decorated with (AsO4) tetrahedra to form a [(SbTi)(AsO4)4O2] chain that extends along the a-direction and defines the cell dimension in this direction at ∼7Å. These chains are cross-linked in the b-direction by chains of edge-sharing (CuO6) octahedra that are decorated by arsenate tetrahedra to form a [Cu2(AsO4OH)2O4] chain; these two chains link to form a sheet parallel to (001). These sheets stack along the c-direction and are linked by (CuO6) and (NaO6) octahedra, together with an extensive network of hydrogen bonds. The [M(TO4)2Φ4] chain (M=octahedrally coordinated metal, T=tetrahedrally coordinated metal, Φ=unspecified simple anion;≡[(SbTi)(AsO4)4O2] chain) is a common motif in secondary oxysalt minerals, occurring in sulfates, phosphates, arsenates, vanadates and silicates. [ABSTRACT FROM AUTHOR]

The title mineral crystallizes in the monoclinic space group C2/m with Z = 4 (single crystal XRD). [ABSTRACT FROM AUTHOR]

The incommensurately modulated crystal structure of the mineral daliranite has been determined using 3D electron diffraction data obtained on nanocrystalline domains. Daliranite is orthorhombic with a = 21, b = 4.3, c = 9.5 Å and shows modulation satellites along c. The solution of the average structure in the Pnma space group together with energy-dispersive X-ray spectroscopy data obtained on the same domains indicate a chemical formula of PbHgAs 2 S 5 , which has one S fewer than previously reported. The crystal structure of daliranite is built from columns of face-sharing PbS 8 bicapped trigonal prisms laterally connected by [2+4] Hg polyhedra and (As 3+ 2 S 5 ) 4- groups. The excellent quality of the electron diffraction data allows a structural model to be built for the modulated structure in superspace, which shows that the modulation is due to an alternated occupancy of a split As site.