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Oscarkempffite, Ag10Pb4(Sb17Bi9)∑ 26S48, a new Sb-Bi member of the lillianite homologous series

Published online by Cambridge University Press:  02 January 2018

Dan Topa ,
Werner H. Paar ,
Emil Makovicky ,
Chris J. Stanley  and
Andy C. Roberts
Dan Topa*
Affiliation:
Natural History Museum-Vienna, Burgring 7, A-1010 Vienna, Austria
Werner H. Paar
Affiliation:
A-5020 Salzburg, Pezoltgasse 46, Austria
Emil Makovicky
Affiliation:
Department of Geoscience and Resource Management, University of Copenhagen, Østervoldgade 10, DK-1350, Copenhagen K, Denmark
Chris J. Stanley
Affiliation:
The Natural History Museum, Cromwell Road, London SW7 5BD, England, UK
Andy C. Roberts
Affiliation:
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A OE8, Canada
*
E-mail: dan.topa@nhm-wien.ac.at
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Abstract

Oscarkempffite, ideally Ag10Pb4(Sb17Bi9)∑=26S48, is a new mineral species found in old material (1929–30) from the Colorada vein, Animas mine, Chocaya Province, Department of Potosi, Bolivia. It is associated with aramayoite, stannite, miargyrite, pyrargyrite and tetrahedrite. Oscarkempffite forms anhedral grains and grain aggregates up to 10 mm across. The mineral is opaque, greyish black with a metallic lustre; it is brittle without any discernible cleavage. In reflected light oscarkempffite is greyish white, pleochroism is distinct, white to dark grey. Internal reflections are absent. In crossed polars, anisotropism is distinct with rotation tints in shades of grey. The reflectance data (%, air) are: 39.9, 42.6 at 470 nm, 38.6, 41.7 at 546 nm, 38.1, 41.2 at 589 nm and 37.3, 40.6 at 650 nm. Mohs hardness is 3–3½, microhardness VHN50 exhibits a range 189–208, with a mean value 200 kg mm–2. The average results of four electron-microprobe analyses in a grain are: Cu 0.24(7), Ag 14.50(8), Pb 11.16(14), Sb 28.72(16), Bi 24.56(17), S 20.87(5), total 100.05(6) wt.%, corresponding to Cu0.24Ag9.92Pb4.00Sb17.36Bi8.64S47.84 (on the basis of Me + S = 88 apfu). The simplified formula, Ag10Pb4Sb17Bi9S48, is in accordance with the results of a crystal-structure determination. The density, 5.8 g cm–3, was calculated using the ideal formula. Oscarkempffite has an orthorhombic cell with a = 13.199(2), b = 19.332(3), c = 8.249(1) Å, V = 2116.3(5) Å3, space group Pnca and Z = 1. The strongest eight lines in the (calculated) powder-diffraction pattern are [d in Å(I)hkl]: 3.66(35)(122), 3.37(70)(132), 3.34(100)(250), 2.982(55)(312), 2.881(86)(322), 2.733(29)(332), 2.073(27)(004) and 2.062(31)(182). Comparison with gustavite, andorite and roshchinite confirms its independence as a mineral species.

Keywords

oscarkempffitesulfosaltnew minerallillianite homologous seriesAnimas mineChocaya ProvinceBolivia
Type
Research Article
Information
Mineralogical Magazine , Volume 80 , Issue 5 , August 2016 , pp. 809 - 817
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2016

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