Abstract

The new mineral janchevite was discovered in Mn-oxide ore from the Kombat mine, Grootfontein district, Otjozondjupa region, Namibia. Associated minerals are baryte, hausmannite, calcite, magnesite, and kombatite. Janchevite forms orange-red thick tabular anhedral to subhedral grains up to 0.4 × 0.8 × 0.8 mm in size. The luster is adamantine. The mineral is brittle, with Mohs' hardness of 2½. Distinct cleavage on {001} is observed. Dcalc = 8.16 g/cm3. The reflectance values [Rmax/Rmin, % (λ, nm)] are: 20.56/20.06 (470), 19.20/18.81 (546), 19.06/18.59 (589), 19.31/18.85 (650). An infrared spectrum indicates the absence of H-bearing groups and indicates V and Mo valences of 5+ and 6+, respectively. The chemical composition is (electron microprobe, wt.%): PbO 91.64, SiO2 0.45, V2O5 1.95, MoO3 2.41, Cl 4.16, –O=Cl –0.94, total 99.67. The empirical formula based on (Pb + V + Mo + Si) = 8 apfu is Pb7.20V5+0.38Mo6+0.29Si0.13Cl2.06O8.25. Janchevite is the V-dominant analogue of parkinsonite. The mineral is tetragonal and its unit-cell parameters as determined from single-crystal X-ray diffraction data are: a 3.9591(5), c 22.6897(3) Å, V 355.65(1) Å3; Z = 1. Powder X-ray diffraction data conform to the space group I4/mmm; the strongest lines of the PXRD pattern [d, Å (I/I0, %) (hkl)] are: 3.889 (24) (011), 3.501 (31) (013), 2.979 (86) (015), 2.833 (25) (008), 2.794 (100) (110), 1.992 (26) (118), 1.988 (49) (020), 1.649 (46) (215). Janchevite is named in honor of the prominent Macedonian mineralogist Prof. Dr. Simeon Janchev (b. 1942).

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