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)Σ3.01Ag2.00S0.99, based on 6 apfu. The name recalls the type locality.
↵1 With the exception of one Au-Ag alloy (“electrum”), mineral nomenclature conforms to minerals approved by the Commission on New Minerals, Nomenclature, and Classification (CNMNC) of the International Mineralogical Association (IMA). The reason is simply that the term is well-known and understood in the mining industry since first used by Pliny the Elder in the year 77. In deportment studies it is useful to differentiate between native gold and “electrum”, especially in view of large differences in density (Kraut & Stern 2000).
↵2 i.e., 80 wt.% of the sample that is smaller than this size.
↵3 Partly due to the abundant contamination from brush hairs.