Kazanskyite, Ba□TiNbNa3Ti(Si2O7)2O2(OH)2(H2O)4, a Group-III Ti-disilicate mineral from the Khibiny alkaline massif, Kola Peninsula, Russia: description and crystal structure

• Published in: Mineralogical Magazine
• Main Authors: CAMARA ARTIGAS, Fernando, Sokolova E, Hawthorne FC
• Other Authors: Cámara F
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: kazanskyite; new mineral; Khibiny alkaline massif; Kola Peninsula; Russia; crystal structure; Group III; Ti-disilicate; TS block; kola peninsula
• Online Access: http://hdl.handle.net/2318/92715; https://doi.org/10.1180/minmag.2012.076.3.03; http://www.minersoc.org/pages/e_journals/minmag.html

Kazanskyite, Ba□TiNbNa3Ti(Si2O7)2O2(OH)2(H2O)4, is a Group-III TS-block mineral from the Kirovskii mine, Mount Kukisvumchorr, Khibiny alkaline massif, Kola Peninsula, Russia. The mineral occurs as flexible and commonly bent flakes 2-15 μm thick and up to 330 μm across. It is colourless to pale tan, with a colourless streak and a vitreous lustre. The mineral formed in a pegmatite as a result of hydrothermal activity. Associated minerals are natrolite, barytolamprophyllite, nechelyustovite, hydroxylapatite, belovite-(La), belovite-(Ce), gaidonnayite, nenadkevichite, epididymite, apophyllite-(KF) and sphalerite. Kazanskyite has perfect cleavage on {001}, splintery fracture and a Mohs hardness of 3. Its calculated density is 2.930 g/cm3. Kazanskyite is biaxial positive with α 1.695, β 1.703, γ 1.733 (λ 590 nm), 2Vmeas. = 64.8(7)°, 2Vcalc. = 55.4°, with no discernible dispersion. It is nonpleochroic. Kazanskyite is triclinic, space group P⎯1, a 5.4260(9), b 7.135(1), c 25.514(4) Å, α 90.172(4), β 90.916(4), γ 89.964(3)°, V 977.61(3) Å3. The strongest lines in the X-ray powder-diffraction pattern [d(Å)(I)(hkl)] are: 2.813(100)(12-4,1-2-2), 2.149(82)(22-2,2-20,207,220,2-22), 3.938(70)(1-13,112), 4.288(44)(11-1,1-10,110,1-11), 2.128(44)(22-3,2-2-1,1-34,221,2-23), 3.127(39)(1-16,115), 3.690(36)(1-14), 2.895(33)(1-23,121) and 2.955(32)(1-20,120,1-22). Chemical analysis by electron microprobe gave Nb2O5 9.70, TiO2 19.41, SiO2 28.21, Al2O3 0.13, FeO 0.28, MnO 4.65, BaO 12.50, SrO 3.41, CaO 0.89, K2O 1.12, Na2O 9.15, H2O 9.87, F 1.29, O = F -0.54, sum 100.07 wt.%, H2O was determined from structure refinement. The empirical formula is (Na2.55Mn0.31Ca0.11Fe2+0.03)Σ3 (Ba0.70Sr0.28K0.21Ca0.03)Σ1.22(Ti2.09Nb0.63Mn0.26Al0.02)Σ3 Si4.05O21.42H9.45F0.59, calculated on 22 (O + F) a.p.f.u., Z = 2. The structural formula of the form AP2MH2MO4(Si2O7)2XO4XP MXPA(H2O)n is (Ba0.56Sr0.22K0.15Ca0.03□0.04)Σ1 (□0.74Ba0.14Sr0.06K0.06)Σ1 (Ti0.98Al0.02)Σ1(Nb0.63Ti0.37)Σ1 ...