Coldwellite, ideally Pd3Ag2S, is a new mineral species discovered in a heavy-mineral concentrate from the Marathon deposit, Coldwell Complex, Ontario Canada. It is cubic, crystallizing in space group P4332 (#212) with a 7.2470(8) Å, V 380.61(1) Å3, Z = 4. The five strongest lines of the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 2.427(100)(221), 2.302(38)(310), 2.195(38)(311), 1.4280(44)(510,431), 0.9294(24)(650,643), and 0.9208(20)(732,651). Associated minerals in the discovery sample include Au-Ag alloy, hollingworthite, isoferroplatinum, keithconnite, kotulskite, mertieite-II, michenerite, palladoarsenide, sobolevskite, sperrylite, stillwaterite, vysotskite, Ti- and Cr-rich magnetite and ilmenite, pyrrhotite, chalcopyrite, and pentlandite, with trace amounts of bornite, cobaltite, and galena. Coldwellite is white with a light pinkish brown tint, and it has a metallic luster. No streak or microhardness could be measured. The mineral shows no internal reflections, pleochroism, bireflectance, or anisotropy. The reflectance values (%) in air for the standard COM wavelengths are: 41.9 (470 nm), 44.9 (546 nm), 44.0 (589 nm), and 45.0 (650 nm). The density, 9.90(1) g/cm3, was calculated using the empirical formula and the unit-cell parameters from the refined crystal-structure. The average result (n = 23) of electron-microprobe analyses is: Pd 56.1, Fe 0.16, Ag 38.2, S 5.63, total 100.09 wt.%, which corresponds to (Pd2.99Fe0.02)∑3.01Ag2.00S0.99, based on 6 apfu. The name recalls the type locality.
Coldwellite, Pd3Ag2S, a New Mineral Species from the Marathon Deposit, Coldwell Complex, Ontario, Canada
Andrew M. McDonald, Louis J. Cabri, Chris J. Stanley, David J. Good, Jason Redpath, Geoff Lane, John Spratt, Doreen E. Ames; Coldwellite, Pd3Ag2S, a New Mineral Species from the Marathon Deposit, Coldwell Complex, Ontario, Canada. The Canadian Mineralogist ; 53 (5): 845–857. doi: https://doi.org/10.3749/canmin.1500020
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