Record details

Title
    Čejkaite, the triclinic polymorph of Na4(UO2)(CO3)3 - a new mineral from Jáchymov, Czech Republic
Statement of responsibility
    Petr Ondruš, Roman Skála, František Veselovský, Jiří Sejkora, Cecilia Vitti
Author
    Ondruš, Petr
    Sejkora, Jiří, 1968-
    Skála, Roman
    Veselovský, František
    Vitti, Cecilia
Language
    anglicky
Source title - serial
    American mineralogist
Vol./nr.
    Vol. 88, no. 4
Pages
    p. 686-693
Year
    2003
Notes
    7 obr., 7 tab., 23 bibl.
    il.
    Zkr. název ser.: Amer. Mineralogist
Subject group
    karbonáty
    krystalochemie
    krystalová struktura
    minerály supergenní
    minerály uranu
    nový minerál
    polymorfie
    recent
    rudy U
    syntéza minerálu
Geographical name
    ČR-Čechy
    Jáchymov (Karlovy Vary)
Keyword
    Czech
    Čejkaite
    Jáchymov
    Mineral
    Na4(UO2)(CO3)3
    New
    Polymorph
    Republic
    Triclinic
Abstract (in english)
   Čejkaite, a new mineral from Jáchymov, NW Bohemia, Czech Republic, forms a thin earthy efflorescence over a calcite vein associated with disintegrated uraninite. The color is pale yellow to beige, the streak is light yellow, and the luster is vitreous. The broad secondary mineral association includes andersonite and schrockingerite. Chemical analysis (by ICP-MS and TG) gave (in wt per cent): Na2O = 21.39, MgO = 0.15, FeO = 0.53, UO3= 53.93, and CO2 = 24.00 (calculated by difference). The simplified chemical formula is Na4UO2(CO3)3. The mineral is triclinic, space group P1 or P1, a = 9.291(2), b = 9.292(2), c = 12.895(2)°A, alfa = 90.73(2), beta = 90.82(2), gama = 120.00(1)°, V = 963.7(4) °A 3, Z = 4, Dmeas= 3.67(1) g/cm3, and Dcalc = 3.766(5) g/cm3.
   The strongest seven lines in the X-ray powder-diffraction pattern [d in °A (I)(hkl)] are: 8.022(92)(l10, 010, 100), 5.080(57)(102, 0l2), 5.024(60)( 112, 112), 4.967(68)( 012, 102), 4.639(100)(120, 210, 110), 3.221(63)(004), 2.681(60) (330, 114, 030, 300). Optical data could not be measured due to the extremely small grain size, but the calculated mean refractive index is 1.5825. Crystal size varies from 0.2 to 0.6 (_m and shows an indistinct hexagonal outline. Thermal decomposition of synthetic čejkaite proceeds in three main steps. DTA endotherm at 430 °C corresponds to the decomposition of the uranyl tricarbonate groups. IR spectrum of čejkaite confirms the presence of crystallographically nonequivalent (CO3)2- groups and the absence of water. The average U-O bond length in (UO2)2+, calculated from v3 = 848 cm-1, is RU-O` 1.81 °A.
   A model based on the crystal structure of trigonal Na4(UO2)(CO3)3 was adopted and applied to solve the čejkaite crystal structure by the Rietveld method (7238 unique reflections, Rp = 0.076, Rwp = 0.104). Uranium is eight-coordinated, and forms a [UO2O6] skeleton with almost linear O-U-O that is roughly perpendicular to an irregular cycle formed by six O atoms that, in turn, belong to three more-or-less regular and planar CO3 groups. Atoms Na 1, Na 1a, and Na2 are octahedrally coordinated, whereas Na3 is pentagonally coordinated. The mineral name honors Jiří Čejka for his notable contributions to the crystal chemistry of U minerals
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    21. 8. 2007
Import date
    8. 8. 2012