• journal_title：American Mineralogist
• Contributor：Yuri P. Men’shikov ; Sergey V. Krivovichev ; Yakov A. Pakhomovsky ; Victor N. Yakovenchuk ; Gregory Yu. Ivanyuk ; Julia A. Mikhailova ; Thomas Armbruster ; Ekaterina A. Selivanova
• Publisher：Mineralogical Society of America
• Date：2006-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2006.2032
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：91
• issue：5-6
• firstpage：922
• section：Articles

Chivruaiite is a new Ca titanosilicate [orthorhombic, Cmmm, a = 7.17(2), b = 22.98(9), c = 6.94(2) Å, V = 1144.4 ų, Z = 1], chemically and structurally related to zorite. The mineral is found in three different hydrothermal veins within the Khibiny and Lovozero alkaline massifs, Kola Peninsula, Russia. It is associated with microcline, eudialyte, natrolite, astrophyllite, aegirine, etc. Chivruaiite occurs as elongate-prismatic crystals (up to 3 mm long) with {100}, {010}, {001}, {101}, and {011} as dominant faces, as well as radiating aggregates. The mineral is transparent, pale-pink to colorless, with vitreous luster and white streak. Cleavage is distinct on {100} and {010}; fracture is step-like. Mohs hardness is about 3. In transmitted light, the mineral is pale-pink, with a faint pleochroism: Z = pale-pink, on X and Y = colorless; dispersion r < v. Chivruaiite is biaxial (+): α =1.705(5), β = 1.627(2), γ = 1.612(2) (for λ = 589 nm), 2V_meas = 40 ± 5°, 2V_calc = 31.7°. Optical orientation: X = b, Y = a, Z = c, D_calc = 2.42 g/cm³, D_meas = 2.40–2.42 g/cm³. The mean chemical composition determined by electron microprobe is (wt%): SiO₂ 45.14; TiO₂ 20.63; Al₂O₃ 0.07; Fe₂O₃ 0.18; MnO 0.02; MgO 0.01; CaO 10.53; Na₂O 0.10; K₂O 1.30; SrO 0.28; Nb₂O₅ 3.63; H₂O 17.30; sum. 99.19. Empirical formula calculated on the basis of Si = 12 is (Ca_3.00K_0.44Na_0.05Sr_0.04Mn_0.01)_∑=3.54(Ti_4.13Nb_0.44Fe³⁺_0.04 Al_0.02)_∑=4.63[Si₁₂O₃₄ |(OH)_4.51O_0.49]·13.08H₂O. Simplified formula is Ca₄(Ti,Nb)₅[(Si₆O₁₇)₂|(OH,O)₅]·13–14H₂O. The strongest X-ray powder-diffraction lines [d in Å, (I), (hkl)] are 11.6 (100) (020), 6.91 (90) (110, 001), 5.23 (50) (130), 3.41 (50) (220), 3.35 (50) (061, 151), 3.04 (80) (221, 240). The structure of chivruaiite was refined to R₁ = 0.038 on the basis of 687 unique observed reflections. It is based upon an open framework of SiO₄ tetrahedra, TiO₆ octahedra, and TiO₅ pyramids. Framework cavities are occupied by Ca²⁺ and K⁺ cations, and H₂O molecules. The mineral is named after its type locality in the Chivruai River valley (the Lovozero massif, Kola Peninsula, Russia). Chivruaiite is a Ca-analog of zorite and ETS-4 and is closely related to haineaultite.