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Litochlebite, Ag (sub 2) PbBi (sub 4) Se (sub 8) , a new selenide mineral species from Zalesi, Czech Republic; description and crystal structure

Jiri Sejkora, Emil Makovicky, Dan Topa, Hubert Putz, Georg Zagler and Jakub Plasil
Litochlebite, Ag (sub 2) PbBi (sub 4) Se (sub 8) , a new selenide mineral species from Zalesi, Czech Republic; description and crystal structure
The Canadian Mineralogist (April 2011) 49 (2): 639-650

Abstract

Litochlebite, Ag (sub 2) PbBi (sub 4) Se (sub 8) , is a new selenide mineral from the Zalesi uranium deposit, Rychlebske hory Mountains, northern Moravia, Czech Republic. It occurs as irregular grains up to 200 mu m, which form aggregates up to 1-2 mm in size in a quartz gangue. These aggregates are replaced along the margins and fractures by a heterogeneous supergene Bi-Se-O phase. Other associated minerals included uraninite, hematite, and uranophane. Litochlebite is opaque, dark grey to black, has a dark grey streak and a metallic luster. No cleavage was observed; the mineral is brittle with an irregular fracture. The VHN (sub 10g) microhardness 230 (227-234) kg/mm (super 2) corresponds to a Mohs hardness of about 3; the calculated density is 7.90 g/cm (super 3) . In reflected light, litochlebite is white, with weak bireflectance (only in oil) and pleochroism from white with a very faint yellowish tint to white with a very faint bluish tint. Between crossed polars, the anisotropy is moderate both in air and in oil, with dark grey to brown polarization-colors. Reflectance values in air (R (sub min) , R (sub max) in %, lambda nm) are: 44.5-49.9 (470), 45.1-50.5 (546), 45.6-51.3 (589), 45.4-51.8 (650). Litochlebite is monoclinic, space group P2 (sub 1) /m, with a 13.182(2), b 4.1840(8), c 15.299(2) Aa, beta 109.11(1) degrees , V 797.3(2) Aa (super 3) , and a:b:c 3.1506:1:3.6565. The main lines of the X-ray powder-diffraction pattern [d in Aa(I)(hkl)] are: 3.684(53) (301), 3.201(76)(104), 3.028(100)(311), 2.980(88)(312) and 2.892(95)(005). Its average composition (electron-microprobe data) is Cu 0.10, Ag 10.27, Cd 0.05, Pb 11.73, Bi 43.27, Se 32.93, S 0.01, total 98.36 wt.%. The resulting empirical formula, written on the basis 15 apfu, is (Ag (sub 1.84) Cu (sub 0.03) ) (sub Sigma 1.87) (Pb (sub 1.09) Cd (sub 0.01) ) (sub Sigma 1.10) Bi (sub 3.99) Se (sub 8.04) . The ideal formula, Ag (sub 2) PbBi (sub 4) Se (sub 8) , requires Ag 11.41, Pb 10.96, Bi 44.22, Se 33.41, total 100.00 wt.%. The crystal structure of litochlebite has been solved by direct methods and refined to R (sub 1) =3.89% on the basis of 938 unique reflections [F (sub o) >4sigma (F (sub o) )] collected on a Bruker AXS diffractometer with a CCD detector and MoKalpha radiation. The crystal structure contains one lead site, four independent Bi sites, four silver sites and eight independent Se sites. One Ag site is an octahedrally coordinated (2 + 4) site in the pseudotetragonal layer, the other Ag site has a distorted tetrahedral coordination. The remaining Ag sites have low occupancies. Litochlebite is an Ag-dominant isotype of watkinsonite, Cu (sub 2) PbBi (sub 4) Se (sub 8) , and structurally related to berryite, Cu (sub 3) Ag (sub 2) Pb (sub 3) Bi (sub 7) S (sub 16) .


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 49
Serial Issue: 2
Title: Litochlebite, Ag (sub 2) PbBi (sub 4) Se (sub 8) , a new selenide mineral species from Zalesi, Czech Republic; description and crystal structure
Affiliation: National Museum, Department of Mineralogy and Petrology, Prague, Czech Republic
Pages: 639-650
Published: 201104
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 25
Accession Number: 2011-059315
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 8 tables
N48°34'60" - N50°28'00", E15°15'00" - E18°49'60"
Secondary Affiliation: University of Copenhagen, DNK, DenmarkParis-Lodron University of Salzburg, AUT, AustriaMasaryk University, CZE, Czech Republic
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201133
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