Tazieffite, Pb20Cd2(As,Bi)22S50Cl10, a new chloro-sulfosalt from Mutnovsky volcano, Kamchatka Peninsula, Russian Federation
International audience Tazieffite, ideally Pb20Cd2(As,Bi)22S50Cl10, is a new mineral from the high-temperature fumaroles of the Mutnovsky volcano, Kamchatka Peninsula, Russian Federation. It occurs as tiny, slender, needle-shaped crystals, up to 400 µm long and 10 µm across, generally forming fibrou...
Published in: | American Mineralogist |
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Main Authors: | , , , , , , , |
Other Authors: | , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
HAL CCSD
2009
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Subjects: | |
Online Access: | https://hal.archives-ouvertes.fr/hal-00433259 https://doi.org/10.2138/am.2009.3190 |
Summary: | International audience Tazieffite, ideally Pb20Cd2(As,Bi)22S50Cl10, is a new mineral from the high-temperature fumaroles of the Mutnovsky volcano, Kamchatka Peninsula, Russian Federation. It occurs as tiny, slender, needle-shaped crystals, up to 400 µm long and 10 µm across, generally forming fibrous aggregates. Tazieffite is closely associated with greenockite, galena, mutnovskite, kudriavite, and Cd-rich cannizzarite. Other minerals spatially associated are pyrite, anhydrite, and cristobalite. Tazieffite is silvery-gray in color, occasionally with a magenta tint when it forms aggregates of extremely fine needles. It has a black streak and metallic luster. In plane-polarized incident light, tazieffite is weakly bireflectant and weakly pleochroic from dark gray to a blue-gray. Between crossed polars, the mineral is weakly anisotropic, without characteristic rotation tints. Reflectance percentages measured in air (Rmin and Rmax) for a single grain are 33.9, 34.1 (471.1 nm), 32.8, 33.0 (548.3 nm), 32.4, 32.6 (586.6 nm), and 30.9, 31.1 (652.3 nm), respectively. Electron microprobe analyses yield the following ranges of concentrations: Pb 41.88–44.14 (avg. 42.90), Cd 0.87–1.16 (avg. 1.03), Sn 0.31–0.69 (avg. 0.48), Bi 20.43–22.94 (avg. 21.90), As 8.64–10.73 (avg. 9.66), S 16.10–17.48 (avg. 16.58), Se 0.82–1.28 (avg. 1.04), Cl 2.39–2.77 (avg. 2.63), Br 0.09–0.15 (avg. 0.12), I 0.27–0.58 (avg. 0.42). The empirical chemical formula, calculated on the basis of 44 cations, is Pb20.06(Cd0.89Sn0.39In0.02)Σ1.30(As12.49Bi10.15)Σ22.64 (S50.08Se1.28)Σ51.36(Cl7.18I0.32Br0.15)Σ7.65. Tazieffite is closely related to the halogen-sulfosalt vurroite, Pb20Sn2Bi22S54Cl6, both from a chemical and structural point of view. It represents the (Cd,As)-dominant of vurroite, according to the coupled heterovalent substitution Sn4+ + 2S2– → Cd2+ + 2Cl–. The crystal structure of tazieffite was refined in the space group C2/c to R = 0.0370 for 4271 reflections with I > 2σ(I). Unit-cell parameters are a = 8.3520(17), b = 45.5920(92), c = ... |
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