A study of nioboloparite samples from the Khibina massif, Kola Peninsula, Russia, demonstrates that the majority is merely calcian niobian loparite-(Ce), niobian calcian loparite-(Ce) or niobian loparite-(Ce). The minerals do not differ in structure or significantly, with respect to their composition, from common loparite-(Ce) that occurs as a primary mineral throughout the Khibina complex. They differ from common loparite-(Ce) in that they are zoned from a Nb-enriched core to a margin enriched in rare-earth elements and depleted in Nb. This zonation trend is the opposite of that developed during crystallization of primary loparite and is considered to reflect reaction of primary relatively Nb-rich loparite with late-stage REE-enriched fluids. One sample of nioboloparite from a pegmatite vein in ijolite-urtite is a lanthanian lueshite characterized by enrichment of La over Ce. The term nioboloparite does not correspond to a distinct mineral species and must be discredited.
The production of electrolytic nickel includes the stage of leaching of captured firing nickel matte dust. The solutions formed during this process contain considerable amounts of Pb, which is difficult to extraction due to its low concentration upon the high-salt background. The sorption of lead from model solutions with various compositions by synthetic and natural titanosilicate sorbents (synthetic ivanyukite-Na-T (SIV), ivanyukite-Na-T, and AM-4) have been investigated. The maximal sorption capacity of Pb is up to 400 mg/g and was demonstrated by synthetic ivanyukite In solutions with the high content of Cl− (20 g/L), extraction was observed only with a high amount of Na (150 g/L). Molecular mechanisms and kinetics of lead incorporation into ivanyukite were studied by the combination of single-crystal and powder X-ray diffraction, microprobe analysis, and Raman spectroscopy. Incorporation of lead into natural ivanyukite-Na-T with the R3m symmetry by the substitution 2Na+ + 2O2− ↔ Pb2+ + □ + 2OH− leds to its transformation into the cubic P−43m Pb-exchanged form with the empirical formulae Pb1.26[Ti4O2.52(OH)1.48(SiO4)3]·3.32(H2O).
Abstract 'Clinobarylite', BaBe 2 Si 2 O 7 , was defined as a monoclinic dimorph of orthorhombic barylite. Subsequently, its crystal structure was also proved to be orthorhombic, differing from barylite in terms of the space group symmetry, Pmn 2 1 instead of Pmnb , and in unit-cell dimensions. Through the order-disorder (OD) theory, the polytypic relationships between 'clinobarylite' and barylite are described. 'Clinobarylite' corresponds to the MDO 1 polytype, with unit-cell parameters a = 11.650, b = 4.922, c = 4.674 Å, space group Pmn 2 1 ; barylite corresponds to the MDO 2 polytype, with a = 11.67, b = 9.82, c = 4.69 Å, space group Pmnb . The re-examination of the holotype specimen of 'clinobarylite' confirmed its orthorhombic symmetry. Its crystal structure has been refined starting from the atomic coordinates calculated for the MDO 1 polytype and the refinement converged to R 1 = 0.0144 for 929 observed reflections [F o > 4σF o ]. Owing to their polytypic relationships, 'clinobarylite' and barylite should be conveniently indicated as barylite-1 O and barylite-2 O , respectively; the name 'clinobarylite' should be discontinued. This new nomenclature of the barylite polytypes has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 13-E).
The structure of shafranovskite, ideally K2Na3(Mn,Fe,Na)4[Si9(O,OH)27](OH)2⋅nH2O (n ∼ 2.33), a K-Na-manganese hydrous silicate from Kola peninsula, Russia, was studied using synchrotron X-ray radiation and a MAR345 image-plate detector at the Swiss-Norwegian beamline of the European Synchrotron Radiation Facility (ESRF, Grenoble, France). The structure [trigonal, space group P31c, a = 14.519(3), c = 21.062(6) Å, V = 3844.9(14) Å3] was solved by direct methods and partially refined to R1 = 0.085 (wR2 = 0.238) on the basis of 2243 unique observed reflections (|Fo| ≥ 4σF). Shafranovskite is a 2:1 hydrous phyllosilicate. Sheets of Mn and Na octahedra (O sheets) are sandwiched between two silicate tetrahedral sheets (T1 and T2). The 2:1 layers are parallel to (001). The upper tetrahedral sheet T1 consists of isolated [Si13(O,OH)37] islands composed of three six-membered rings. The octahedral sheet O consists of Mnφ6, Na1φ6, and Na2φ6 octahedra (φ = O, OH, H2O). This unit can be considered as a trioctahedral sheet with each 20th octahedron vacant. The lower tetrahedral sheet T2 consists of [Si13(O,OH)37] islands linked into a sheet through an additional SiO3OH tetrahedron. The Na3, K1, K2 atoms, and H2O32 groups are between the 2:1 layers and provide their linkage along c.
Abstract Two quintinite polytypes, 3 R and 2 T , which are new for the Kovdor alkaline-ultrabasic complex, have been structurally characterized. The crystal structure of quintinite-2 T was solved by direct methods and refined to R 1 = 0.048 on the basis of 330 unique reflections. The structure is trigonal, P $\bar 3$ c 1, a = 5.2720(6), c = 15.113(3) Å and V = 363.76(8) Å 3 . The crystal structure consists of [Mg 2 Al(OH) 6 ] + brucite-type layers with an ordered distribution of Mg 2+ and Al 3+ cations according to the $\sqrt 3 $ × $\sqrt 3 $ superstructure with the layers stacked according to a hexagonal type. The complete layer stacking sequence can be described as … =Ab 1 C = Cb 1 A =…. The crystal structure of quintinite-3 R was solved by direct methods and refined to R 1 = 0.022 on the basis of 140 unique reflections. It is trigonal, R $\bar 3$ m , a = 3.063(1), c = 22.674(9) Å and V = 184.2(1) Å 3 . The crystal structure is based upon double hydroxide layers [ M 2+,3+ (OH) 2 ] with disordered distribution of Mg, Al and Fe and with the layers stacked according to a rhombohedral type. The stacking sequence of layers can be expressed as … =АB = BC = CA =… The study of morphologically different quintinite generations grown on one another detected the following natural sequence of polytype formation: 2 H → 2 T → 1 M that can be attributed to a decrease of temperature during crystallization. According to the information-based approach to structural complexity, this sequence corresponds to the increasing structural information per atom ( I G ): 1.522 → 1.706 → 2.440 bits, respectively. As the I G value contributes negatively to the configurational entropy of crystalline solids, the evolution of polytypic modifications during crystallization corresponds to the decreasing configurational entropy. This is in agreement with the general principle that decreasing temperature corresponds to the appearance of more complex structures.
