Affiliation:
1. 514 Queen Elizabeth Driveway, Ottawa, Ontario K1S 3N4, Canada
2. Harquail School of Earth Sciences, Laurentian University, 935 Ramsey Lake Road, Sudbury, Ontario P3E 2C6, Canada
3. Institute of Ore Deposits, Geology, Petrography, Mineralogy and Geochemistry, Straromonetny Street, 35, Moscow 109017, Russia
Abstract
Abstract
A re-examination by electron probe microanalysis of the holotype sample of the platinum-group mineral borishanskiite, previously defined as Pd1+x(As,Pb)2 with x = 0–0.2, reveals that the mineral contains no detectable As. The new data also show the mineral to be stoichiometric, i.e., vacancy-free, with the average chemical composition (based on 2 apfu) of Pd0.99(Pb0.72Bi0.28)Σ1.00 (n = 3) or ideally, PdPb. A comparison of the powder X-ray diffraction patterns for borishanskiite (PDF 00-029-0960) and polarite (PDF 00-023; ideally PdPb) show that, within error, the two are same. Further, the refined unit-cell parameters of borishanskiite, a = 7.18(2), b = 8.62(2), c = 10.66(2) Å, agree well with those of polarite, a = 7.140, b = 8.563, c =10.501 Å. Given the new chemical data for borishanskiite, which suggest the ideal chemical formula PdPb, along with its crystallographic similarity to polarite, it is concluded that borishanskiite is equivalent to polarite. Discussion of the extent of the PdBi–PdPb solid-solution series and confusion concerning the ideal formula for polarite is also presented.
Publisher
Mineralogical Association of Canada
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