Saamite, Ba□TiNbNa3Ti(Si2O7)2O2(OH)2(H2O)2, a group-III Ti-disilicate mineral from the Khibiny Alkaline Massif, Kola Peninsula, Russia: description and crystal structure

• Published in: The Canadian Mineralogist
• Main Authors: CAMARA ARTIGAS, Fernando, Sokolova E, Abdu YA, Hawthorne FC
• Other Authors: Cámara F
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2014
• Subjects: saamite; new mineral; Khibiny alkaline massif; Kola Peninsula; Russia; crystal structure; Group III; Ti-disilicate; TS block; kola peninsula
• Online Access: http://hdl.handle.net/2318/155526; https://doi.org/10.3749/canmin.1400043; http://www.canmin.org/

Saamite, Ba□TiNbNa3Ti(Si2O7)2O2(OH)2(H2O)2, is a Group-III TS-block mineral from the Kirovskii mine, Mount Kukisvumchorr, Khibiny alkaline massif, Kola Peninsula, Russia. The mineral occurs as transparent platy crystals 2–10 μm thick and up to 180 μm across. It is colorless to very pale tan, with a white streak and a vitreous luster. The mineral formed in a pegmatite as a result of hydrothermal activity. Associated minerals are natrolite, barytolamprophyllite, kazanskyite, nechelyustovite, hydroxylapatite, belovite-(La), belovite-(Ce), gaidonnayite, nenadkevichite, epididymite, apophyllite-(KF), and sphalerite. Saamite has perfect cleavage on {001}, uneven fracture and a Mohs hardness ca. 3. Its calculated density is 3.243 g/cm3. Saamite is biaxial positive with α 1.760, β 1.770, γ 1.795 (λ 589 nm), 2Vmeas. = 69(2)°, 2Vcalc. = 65°, with medium dispersion, r > v. It is nonpleochroic. Saamite is triclinic, space group PFormula , a 5.437(2), b 7.141(3), c 21.69(1) Å, α 92.97(1), β 96.07(1), γ 90.01(1)°, V 836.3(11) Å3. The strongest lines in the X-ray powder-diffraction pattern [d(Å)(I)(hkl)] are: 21.539(100)(001), 2.790(15)(122), 2.692(14)(008), 3.077(13)(007), 7.180(11)(003), 2.865(11)(1Formula 2), 1.785(9)(1Formula 4), 2.887(9)(Formula 22, 0Formula 7, 115), and 1.785(9)(0Formula 1, 1Formula 7, 040, Formula Formula 8, 230, 23Formula ). Chemical analysis by electron microprobe gave Nb2O5 12.24, TiO2 20.37, SiO2 29.07, Al2O3 0.08, FeO 0.32, MnO 5.87, MgO 0.04, BaO 11.31, SrO 2.51, CaO 1.76, K2O 0.77, Na2O 8.39, H2O 5.77, F 1.71, O = F −0.72, sum 99.49 wt.%; H2O was determined from structure refinement and its presence was confirmed by IR spectroscopy. The empirical formula based on 20 (O + F) atoms pfu is (Ba0.61Sr0.20K0.13□0.06)Σ1(□0.74Ca0.26)Σ1Formula (Ti2.09Nb0.76Mn0.13Mg0.01Al0.01)Σ3Si3.97O19.26H5.26F0.74, Z = 2. The simplified formula is as follows: Ba(□,Ca)Ti(Nb,Ti)(Na,Mn)3(Ti,Nb)(Si2O7)2O2(OH,F)2(H2O)2. The IR spectrum of saamite contains the following bands: ~1605, 1645, ~1747 and ~3420 cm−1. The crystal ...