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Hansblockite, (Cu,Hg)(Bi,Pb)Se2, the monoclinic polymorph of grundmannite: a new mineral from the Se mineralization at El Dragón (Bolivia)

Published online by Cambridge University Press:  02 January 2018

Hans-Jürgen Förster ,
Luca Bindi ,
Chris J. Stanley  and
Günter Grundmann
Hans-Jürgen Förster*
Affiliation:
Helmholtz Centre Potsdam German Research Centre for Geosciences GFZ, D-14473 Potsdam, Germany
Luca Bindi
Affiliation:
Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira 4, I-50121 Firenze, Italy
Chris J. Stanley
Affiliation:
Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
Günter Grundmann
Affiliation:
Eschenweg 6, D-32760 Detmold, Germany
*
*E-mail: [email protected]
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Abstract

Hansblockite, ideally (Cu,Hg)(Bi,Pb)Se2, is a new selenide from the El Dragón mine, Bolivia. It typically occurs in thin subparallel plates intergrown with two unnamed Cu–Hg–Pb–Bi–Se species, clausthalite, Corich penroseite and petrovicite.It also forms subhedral to anhedral grains up to 150 μm long and 50 μm wide. Hansblockite is non-fluorescent, black and opaque with a metallic lustre and black streak. It is brittle, with an irregular fracture and no obvious parting and cleavage. The VHN20 values range from37 to 50 (mean 42) kg mm–2 (Mohs hardness 2–2½). In plane-polarized incident light, hansblockite is cream to light grey in colour, weakly bireflectant and weakly pleochroic from greyish cream to cream. Under crossed polars, hansblockite is weakly anisotropic withkhaki to pale blue rotation tints. The reflectance values in air for the Commission on Ore Mineralogy (COM) standard wavelengths are: 47.3–48.1 (470 nm), 47.4–49.9 (546 nm), 47.1–49.0 (589 nm) and 46.6–48.5 (650 nm). The mean composition is Cu 9.31, Ag 0.73, Hg 11.43,Pb 3.55, Ni 0.17, Co 0.03, Bi 31.17, Se 34.00, total 100.39 wt.%. The mean empirical formula (based on 4 apfu) is (Cu0.68Hg0.27Ag0.03Ni0.01)∑=0.99(Bi0.69Pb0.31)∑=1.00Se2.01. The simplifiedformula is (Cu,Hg) (Bi,Pb)Se2. Hansblockite is monoclinic, space group P21/c, with a = 6.853(1), b = 7.635(1), c = 7.264(1) Å, β = 97.68(1)°, V = 376.66(9) Å3 and Z = 4. Density is 8.26 gcm–3. The five strongest powder X-ray diffraction lines [d in Å (I/I0) (hkl)] are: 3.97 (90) (111), 3.100 (40) (121), 2.986 (100) (211), 2.808 (50) (112) and 2.620 (50) (022). Hansblockite represents the monoclinic polymorph ofgrundmannite, CuBiSe2, with Hg and Pb being essential in stabilizing the monoclinic structure via the coupled substitution Cu+ + Bi3+⇔ Hg2+ + Pb2+. The mineral name is in honour of Hans Block (1881–1953), in recognition of hisimportant role in boosting Bolivian ore mining.

Keywords

hansblockitenew mineral specieschemical compositioncrystal structureseleniumEl DragónBolivia
Type
Research Article
Information
Mineralogical Magazine , Volume 81 , Issue 3 , June 2017 , pp. 629 - 640
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2017

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