Contribution to the crystal chemistry of lead-antimony sulfosalts: Systematic Pb-versus-Sb crossed substitution in the plagionite homologous series, Pb2N-1(Pb1-xSbx)2(Sb1-xPbx)2Sb6S13+2N

The plagionite homologous series contains four well-defined members with the general formula Pb1+2NSb8S13+2N: fülöppite (N = 1), plagionite (N = 2), heteromorphite (N = 3), and semseyite (N = 4). The crystal structure of several natural and synthetic samples of fülöppite, plagionite, and semseyite have been refined through single-crystal X-ray diffraction, confirming the systematic Pb-versus-Sb crossed substitution observed previously in semseyite and fülöppite. This crossed substitution takes place mainly in two adjacent cation sites in the middle of the constitutive SnS-type layer. The substitution coefficient x appears variable, even for a given species, with the highest values observed in synthetic fülöppite samples. The developed structural formula of the plagionite homologues can be given as Pb2N-1(Pb1-xSbx)2(Sb1-xPbx)2Sb6S13+2N. In the studied samples, x varies between ∼ 0.10 and 0.40. In the ribbons within the SnS-type layer, (Pb=Sb) mixing can be considered the result of the combination, in a variable ratio, of two cation sequences, i.e. (Sb-Sb-Sb)-Pb-Sb-(..), major in plagionite and semseyite, and (Sb-Sb-Sb)-Sb-Pb-(..), major in fülöppite and, probably, in heteromorphite. The published crystal structure of synthetic "Pb-free fülöppite"is revised according to this approach. It would correspond to a Na derivative, with a proposed structural formula of (Na0.5Sb0.5)(Na0.2Sb0.8)2(Na0.3Sb0.7)2Sb6S15, ideally Na1.5Sb9.5S15. In fülöppite, increasing x induces a flattening of the unit cell along c, with a slight volume decrease. Such a general Pb-versus-Sb crossed substitution would attenuate steric distortions in the middle of the SnS-type layer of the plagionite homologous series. Crystallization kinetics seem the main physical factor that controls such an isochemical substitution

Jamesonite delle miniere di Fornovolasco (Vergemoli, Lucca) : primo ritrovamento sulle Alpi Apuane

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(Mn1-xPbx)Pb10+ySb12-yS26-yCl4+yO, a new oxy-chloro-sulfide with similar to 2nm-spaced (Mn,Pb)Cl-4 single chains within a waffle-type crystal structure

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Zvěstovite-(Zn), Ag 6(Ag 4Zn 2)As 4S 13, a new tetrahedrite-group mineral from Zvěstov, Czech Republic

The new mineral, zvěstovite-(Zn), ideally Ag6(Ag4Zn2)As4S13, was found in quartz-baryte gangue at the mine dump of the abandoned small deposit of Zvěstov, central Bohemia, Czech Republic. Zvěstovite-(Zn) is associated with tennantite-(Zn), tetrahedrite-(Zn), argentotennantite-(Zn), acanthite and supergene azurite and malachite. The new mineral occurs as rare relic anhedral grains rimmed by acanthite, up to 100 μm in size. Zvěstovite-(Zn) is grey, Mohs hardness is ca. 3½-4, in agreement with other members of the tetrahedrite group; the calculated density is 5.16 g.cm-3. In reflected light, zvěstovite-(Zn) is grey with a greenish tint, without bireflectance, pleochroism or anisotropy. Deep red internal reflections are ubiquitous. Reflectance values of zvěstovite-(Zn) in air (R%) are: 28.5 at 470 nm, 26.9 at 546 nm, 25.5 at 589 nm and 23.8 at 650 nm. The empirical formula for zvěstovite-(Zn), based on electron-microprobe analyses (n = 4), is Ag6.27[(Ag3.90Cu0.38)Σ4.28(Zn1.60Fe0.09Cd0.03)Σ1.72]Σ6.00(As2.26Sb1.48)Σ3.74S12.50. The ideal formula is Ag6(Ag4Zn2)As4S13, which requires (in wt.%) Ag 56.01, Zn 6.79, As 15.56 and S 21.64, total 100.00. Zvěstovite-(Zn) is cubic, I3m, with unit-cell parameters: a = 10.850(2) Å, V = 1277.3(8) Å3 and Z = 2. The strongest reflections of the calculated powder X-ray diffraction pattern [d, Å (I) (hkl)] are: 3.1321(100) (222), 2.7125(21) (400), 1.9809(11) (521), 1.9180(31) (440) and 1.6357(15) (622). According to the single-crystal X-ray diffraction data (Robs = 0.051), the crystal structure of zvěstovite-(Zn) agrees with the general features of the members of the tetrahedrite group. Zvěstovite-(Zn) is named after its type locality, Zvěstov; the suffix indicates the dominant divalent C-constituent, according to the approved nomenclature of the tetrahedrite group. It is the As-isotype of rozhdestvenskayaite-(Zn). The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2020-061)

LEAD-ANTIMONY SULFOSALTS FROM TUSCANY. IX MARRUCCIITE, Hg3Pb16Sb18S46, A NEW SULFOSALT FROM BUCA DELLA VENA MINE. APUAN ALPS: DEFINITION AND CRYSTAL STRUCTURE

Marrucciite, Hg3Pb16Sb18S46, is a new sulfosalt discovered in the Fe-Ba deposit of Buca della Vena, Apuan Alps (Italy). It occurs as black acicular metallic crystals in calcite veins; reflectance values in air are (R %; λ nm): 33.1 (470), 30.0 (546), 28.8 (589), 26.5 (650). Marrucciite is monoclinic, space group C2/m, with a 48.32(1) Å, b 4.117(1) Å, c 24.056(5) Å, β 118.84(3)°, V 4192(3) Å3, Z = 2, Dcalc. = 6.00 g/cm3; a 2b superstructure is present. Main lines of the X-ray diffraction powder pattern [d (in Å), I (main hkl)]: 4.02, 33 (12.0.3, 802); 3.480, 64 (803, 604); 3.418, 88 (607, 10.0.2, 314) ; 3.106, 31 (9.1.4); 2.994, 100 (11.1.2); 2.922, 41 (11.1.1); 2.056, 52 (020); 1.764, 41 (627). Electron microprobe analysis gave (wt.%; mean of 4 spot analyses): Cu 0.18(12), Hg 7.90(9), Pb 42.41(7), Sb 29.71(7), S 19.47(18), Cl 0.06(2), sum 99.73(14). The chemical formula (basis: 46 (S + Cl) at.) is Cu0.21Hg2.98Pb15.46Sb18.44S45.87Cl0.13, giving the stoichiometric one Hg3Pb16Sb18S46 that fulfils the charge balance. X-ray single crystal study (R = 9.56 %) revealed a complex structure, with Hg in two specific distorted octahedral coordinations (2 short distances each, close to 2.36 Å A). There are 40 other independent positions: 7 Pb, 2 (Pb, Sb), 8 Sb and 23 S. The general architecture of the structure is strongly related to that of hexagonal Ba12Bi24S48, with three types of Me10S14 rods (× 2) around a HgSb2Pb4S4 central column. It explains the pseudo-hexagonal symmetry (a/2 ∼ c; β ∼ 120°). A strong topologic relationship exists also between marrucciite and scainiite. Like rouxelite, the other coexisting Hg bearing sulfosalt, marrucciite was formed by hydrothermal process during the Apenninic tectono-metamorphic event

Lead-antimony sulfosalts from Tuscany (Italy). VIII. Rouxelite, Cu2HgPb22Sb28S64(O,S)2, a new sulfosalt from Buca della Vena mine, Apuan Alps: definition and crystal structure

Rouxelite, Cu2HgPb22Sb28S64(O,S)2, is a new species of sulfosalt discovered in the Buca della Vena Fe–Ba deposit, Apuan Alps, Italy. It occurs as acicular metallic crystals in calcite veins; refl ectance values in air are (R%, in nm): 38.2 (470), 36.2 (546), 35.4 (589), 32.8 (650). Rouxelite is monoclinic, space group C2/m, with a 43.113, b 4.059, c 37.874 Å, 117.35°, V 5887 Å3, Z = 2, Dcalc = 5.86 g/cm3. The eight most intense lines of the X-ray powder-diffraction pattern [d (in Å)(I)(hkl)] are: 3.84(31)(1 — 0.0.8), 3.402(100)(1 — 0.0.2, 1 — 2.0.8, 115), 3.369(74)(¯714, 0.0.10), 2.815(70)(317, 1 — 1.1.4), 2.756(36)(516, 12.0.3), 2.251(31)(1.1.12, 3.1.11), 2.116(31)(1 — 1.1.15), and 1.955(30)(1 — 9.1.5, 11.1.8). Electron-microprobe analyses gave (wt.%; mean of six spot analyses): Cu 1.34(5), Hg 1.76(9), Pb 45.08(15), Sb 31.50(14), S 20.07(11), O (struct.) 0.20, sum 99.95. The chemical formula, calculated on the basis of a cation total of 53 atoms, is Cu2.20Hg0.92Pb22.78Sb27.10S65.53O1.31 (Z = 2), giving the idealized formula Cu2HgPb22Sb28S64(O,S)2, which is charge-balanced. An X-ray single-crystal study, despite a poor R value (0.169), revealed a quite original structure, with Cu and Hg in two specifi c sites, a tetrahedral one for Cu, and a fl attened octahedral one for Hg. There is also a split O,S position, bound to two Sb atoms. For the main part, Pb, Sb and S atoms are organized in columns with a pseudoternary axis, derived from hexagonal Ba12Bi24S48. The structural formula is Cu2HgPb22.6Sb27.4S64.67O1.33. The structure is built up of two types of ribbons parallel to b and alternating along a, rimmed by a ribbon-layer parallel to (010); the result is a three-component structure of the boxwork type, like for neyite. Very large topologically equivalent columns are also recognizable in rouxelite and kobellite, which have about 90% of their structure motif in common. The formation of rouxelite is associated with the hydrothermal remobilization and deposition of mercury in the Apuan Alps during the Apenninic tectonometamorphic event, as illustrated in the nearby Hg deposits of Ripa and Levigliani. The name honors Jean Rouxel (1935–1998), solid state chemist, professor and founder of the Institut des Matériaux, University of Nantes (France)