Findings of bismuthocolumbumite in myarolite granite pegmatites of the Rangkul pegmatite field in the Eastern Pamirs, Gorno-Badakhshan Autonomous Area, Tajikistan are described. The mineral was found in the form of crystals up to 2 cm in the myarol cavities of the pegmatite veins Mika, Malysh and in the form of sprouts of 20–30 μm in Sc-containing columbite-Mn in intergrowth with eschinitis- (Y) in the near-myarol complex of pegmatite Dorozhny. The crystals were measured on a goniometer; the calculated and measured coordinates of the faces are given (in the setup a <c <b). The habitus of the crystals is prismatic, determined by the faces of the rhombic prism m {110}; minor and weakly expressed faces of the prismatic belt: pinacoid {010}, prisms {130}, {150}, {160}, {170}; the usual faces of the head are the rhombic prism i {101} and the dipyramid u {111}, the more rare prism f {032}. The color of bismuthocolumbite in crystals is dark brown, almost black, shines reddish-brown, in small fragments reddish-brown to light brown. The trait is light brown. Cleavage perfect according to (010). The measured density, g / cm3, 7.36 (1) (Kid), 7.61 (1) (Mika). Optically biaxial (+), 2V = 70 (10) °, the dispersion is strong, r> v. The plane of the optical axes is perpendicular to the (010) plane. The refractive indices of bismuthocolumbite from Mick's pegmatite: np = 2.42 (1), nm = 2.45 (1), ng = 2.50 (2). In reflected light, gray with a faint bluish tint, medium reflectivity, strong anisotropy, strong reflections from yellow to reddish-brown. Reflection spectra are given. Microhardness VHN100 = 360 (Kid), 353 (Mika). 6 m. analyzes. Chem. composition (wt.%, selective an., Kid, Mika, Dorozhniy): Ta2O5 2.11, 11.66, 8.61; Nb2O5 35.54, 28.11, 8.61; WO3 0.08, 0.11, 3.60; TiO2 0.02, 0.00, 0.58; PbO 0.10, 0.10, 0.00; SnO2 0.03, 0.12, 0.00; MnO 0.00, 0.01, 0.26; FeO 0.03, 0.00, 0.11; Sb2O3 0.78, 1.77, 8.55; Bi2O3 62.50, 57.59, 49.75; amount 101.19, 99.47, 100.10. X-ray powder diffraction patterns are shown. Parameters of the rhombic unit cell (Å): a = 4.982 (2), b = 11.719 (4); c = 5.677 (2) (Kid); a = 4.981 (2), b = 11.746 (4); c = 5.670 (2) (Mika). Possible reasons for the rarity of bismuthocolocolumbite as compared to stibiocolumbite and their Ta analogues are discussed. читать далее...
Smolyaninova V.N.
Devoted to the 110th anniversary of the birth of Natalia Nikolaevna Smolyaninova, pp. 1-18
