Vadlazarenkovite, Pd8Bi1.5Te1.25As0.25, a new mineral isotypic with mertieite from the Konder massif, Far East, Russia

The new mineral vadlazarenkovite, ideally Pd8Bi1.5Te1.25As0.25, was discovered in a heavy concentrate obtained from ore samples collected at the Anomal'noe occurrence, Konder alkaline-ultrabasic massif, Khabarovsk Krai, Far East, Russia. It occurs as anhedral grains up to 0.15 × 0.15 mm, intergrown with vysotskite and associated with numerous platinum-group element (PGE) bearing minerals (arsenopalladinite, ezochiite, hollingworthite, kotulskite, norilskite, polarite, skaergaardite, sobolevskite, sperrylite, törnroosite, zvyagintsevite etc.). Vadlazarenkovite is grey, opaque with metallic lustre, has brittle tenacity and uneven fracture. No cleavage and parting are observed. The Vickers' micro-indentation hardness (VHN, 50 g load) is 424 kg/mm2 (range 406-443, n = 4), corresponding to a Mohs' hardness of 4.5-5. Dcalc. = 11.947 g/cm3. In reflected light, vadlazarenkovite is white with a pale creamy hue. The bireflectance is weak in air and noticeable in oil immersion. In crossed polars the new mineral exhibits distinct anisotropy in grey tones. The reflectance values for wavelengths recommended by the Commission on Ore Mineralogy of the International Mineralogical Association are (Rmin/Rmax, %): 47.2/47.8 (470 nm), 49.1/50.8 (546 nm), 50.7/52.6 (589 nm) and 52.4/54.6 (650 nm). The chemical composition (wt.%, electron microprobe data, mean of 6 analyses) is: Pd 63.67, Ag 2.21, As 1.27, Sb 0.60, Te 11.26, Pb 2.56, Bi 19.95, total 101.51. The empirical formula calculated on the basis of 11 atoms per formula unit is (Pd7.87Ag0.27)Σ8.14(Bi1.26Te1.16As0.22Pb0.16Sb0.06)Σ2.86. Vadlazarenkovite is trigonal, space group R c, a = 7.7198(2), c = 43.1237(11) Å, V = 2225.66(13) Å3 and Z = 12. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 2.308 (55) (1 1 15); 2.262 (100) (2 0 14); 2.232 (70) (3 0 0); and 2.040 (70) (1 1 18). The crystal structure of vadlazarenkovite was refined to R1 = 0.0267 for 761 reflections with Fo > 4σ(Fo). The new mineral is isotypic with mertieite. It honours Professor Vadim Grigorievich Lazarenkov (1933-2014) for his outstanding contributions to the geology, geochemistry and mineralogy of platinum-group elements.