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).
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
ORLANDI, PAOLO;
2005-01-01
Abstract
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).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
