Verbeekite, monoclinic PdSe₂, a new mineral from the Musonoi Cu-Co-Mn-U mine, near Kolwezi, Shaba Province, Democratic Republic of Congo

Authors: Roberts A. C.; Paar W. H.; Cooper M. A.; Topa D.; Criddle A. J.; Jedwab J.

Source: Mineralogical Magazine, Volume 66, Number 1, 1 February 2002 , pp. 173-179(7)

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Abstract:

Verbeekite, ideally PdSe₂, monoclinic with space-group choices C2/m, C2 or Cm; a = 6.659(7), b = 4.124(5), c = 4.438(6) Å, ß = 92.76(3)°, V = 121.7(4) Å³; a:b:c = 1.6147:1:1.0761, Z = 2, is a new, very rare, primary mineral, intimately associated with secondary oosterboschite {(Pd,Cu)₇Se₅}, from the Musonoi Cu-Co-Mn-U mine, near Kolwezi, Shaba Province, Democratic Republic of Congo. Additional associated minerals are Cu- and Pd-bearing trogtalite {(Co,Cu,Pd)Se₂}, Se-bearing digenite and Se-bearing covellite. The strongest five lines of the X-ray powder-diffraction pattern {d in Å (I) (hkl)} are: 4.423(30)(001), 3.496 (30)(110), 2.718(100)(111), 1.955(50)(310) and 1.896(50)(l¯12). The mineral has also been identified, as a single anhedral 25 µm-sized grain, from Hope's Nose, Torquay, Devon, England where it is associated with native gold, chrisstanleyite Ag₂Pd₃Se₄, oosterboschite(?), unnamed Pd₂HgSe₃ and cerussite. At Musonoi, altered verbeekite grains do not exceed 200 µm in size and are anhedral, black, with a black streak and a metallic lustre. The mineral is opaque, brittle, has an uneven fracture, and lacks discernible cleavage. The VHN₅ ranges 490–610, mean 550 kp/mm² (2 indentations), roughly approximating a Mohs' hardness of 5Ý. D_calc. = 7.211 g/cm³ for the ideal formula. Electron-microprobe analyses (mean of 4 spot analyses) yielded Pd 39.6, Cu 0.5, Se 58.8, total 98.9 wt.%. The empirical formula is (Pd_0.99Cu_0.02)_1.01Se_1.99, based on Pd+Cu+Se = 3. In plane-polarized reflected light, the mineral is a nondescript grey and is neither pleochroic nor perceptibly bireflectant. Anisotropy is moderate with rotation tints in varying shades of brown. Reflectance spectra and colour values are tabulated. The name honours Dr Théodore Verbeek (1927–1991) who was the first geoscientist to study the Musonoi palladium mineralization in the Democratic Republic of Congo (1955–1967) and who co-discovered this new mineral phase.

Keywords: VERBEEKITE; PALLADIUM DISELENIDE; X-RAY DATA; ELECTRON-MICROPROBE DATA; REFLECTANCE DATA; MUSONOI CU-CO-MN-U MINE; KOLWEZI; SHABA PROVINCE; DEMOCRATIC REPUBLIC OF CONGO; HOPE'S NOSE; TORQUAY; DEVON; ENGLAND