Ekaterina A. Selivanova

Ivanyukite-Na-T, ivanyukite-Na-C, ivanyukite-K, and ivanyukite-Cu: New microporous titanosilicates from the Khibiny massif (Kola Peninsula, Russia) and crystal structure of ivanyukite-Na-T

Abstract Ivanyukite-Na-T, Na3[Ti4(OH)O3(SiO4)3]·7H2O, ivanyukite-Na-C, Na2[Ti4O2(OH)2(SiO4)3]·6H2O, ivanyukite-K, K2[Ti4(OH)2O2(SiO4)3]·9H2O, and ivanyukite-Cu, Cu[Ti4(OH)2O2 (SiO4)3]·7H2O, are new microporous titanosilicates found in a natrolitized microcline-aegirine-sodalite lens in the orthoclase-bearing urtite at the Koashva Mountain (Khibiny Massif, Kola Peninsula, Russia). The minerals occur as well-shaped colorless (ivanyukite-Na-T), paleorange (ivanyukite-Na-C), pale-blue (ivanyukite-K), and green (ivanyukite-Cu) cubic crystals (up to 1.5 mm in diameter) grown on microcline, vinogradovite, sazykinaite-(Y), natrolite, and djerfisherite. The minerals have vitreous luster and white streak. They are transparent and non-fluorescent. The Mohs hardness is estimated as ~4. The minerals are brittle. Cleavage is perfect on {100} (ivanyukite-Na-C, ivanyukite-K, and ivanyukite-Cu) or on {1011} (ivanyukite-Na-T), fracture is stepped. Density, measured by the sink/float method in heavy liquids, ranges from 2.60 (ivanyukite-Na-C) to 2.70 g/cm3 (ivanyukite-Na-T, ivanyukite-K, and ivanyukite-Cu), whereas calculated densities are: 2.58 (ivanyukite-Na-T), 2.39 (ivanyukite-Na-C), 2.69 (ivanyukite-K), and 2.46 g/cm3 (ivanyukite- Cu). Ivanyukite-Na-T is uniaxial (+), nω = 1.76(1), nε = 1.85(9) (589 nm), and the other minerals are isotropic, n = 1.73(1). Chemical analysis by electron microprobe gave (wt% for ivanyukite-Na-T, ivanyukite-Na-C, ivanyukite-K, and ivanyukite-Cu, respectively): Na2O 7.46, 5.19, 0.27, and 0.17; Al2O3 0.07, 0.21, 0.18, and 0.07; SiO2 23.75, 25.47, 23.16, and 24.80; SO3 0.00, 0.00, 0.00, and 0.20; K2O 5.89, 6.34, 7.09, and 6.81; CaO 0.21, 0.14, 0.95, and 0.23; TiO2 38.89, 37.81, 36.14, and 38.36; MnO 0.05, 0.33, 0.68, and 0.28; FeO 0.54, 2.17, 0.37, and 0.73; CuO 0.00, 0.00, 2.21, and 6.81; SrO 0.00, 0.00, 0.19, and 0.00; Nb2O5 2.99, 2.90, 3.62, and 3.02; BaO 0.14, 0.00, 0.00, and 0.00; H2O (by the Penfield method) 19.00, 19.15, 25.00, and 21.50; total 98.99, 99.71, 99.86, and 98.97. The empirical formulae (based on Si+Al = 3 apfu) are (Na1.82 K0.95 Ca0.03 Ba0.01)Σ2.81[(Ti3.68 Nb0.17 Fe0.06 Mn0.01)Σ3.92(Si2.99 Al0.01)Σ3.00O14.59(OH)1.37]·7.29H2O (ivanyukite-Na-T), (Na1.17K0.94Ca0.03)Σ2.14[(Ti3.32Fe0.21Nb0.15Mn0.03)Σ3.71(Si2.97Al0.03)Σ3.00 O12.89(OH)2.87]·6.01H2O (ivanyukite-Na-C), (K1.16Cu0.21Ca0.13Na0.07Sr0.01)Σ1.58[(Ti3.49Nb0.21Mn0.07Fe0.04)Σ3.81(Si2.97Al0.03)Σ3.00 O13.19(OH)2.75]·9.32H2O (ivanyukite-K), and (Cu0.62K0.43Na0.04Ca0.03)Σ1.12[(Ti3.48Nb0.16Fe0.07Mn0.03)Σ3.74(Si2.99Al0.01)Σ3.00 O12.88(OH)2.88(SO4)0.02]·7.21H2O (ivanyukite-Cu). Ivanyukite-Na-T is trigonal, R3m, a = 10.94(2), c = 13.97(4) Å, Z = 3. Other minerals are cubic, P4̅3m a = 7.856(6) (ivanyukite-Na-C), 7.808(2) (ivanyukite-K), and 7.850(7) Å (ivanyukite-Cu); Z = 1. The strongest lines in the powder X-ray diffraction pattern [dbs(Å) (Iobs) hkl] are: 7.88(100) (011), 3.277(60)(014), 3.175(80)(212), 2.730(50)(220), 2.607(70)(303), 2.471(50)(124), 1.960(60)(044), 1.916(50) (135) (ivanyukite-Na-T); 7.88(100)(100), 4.53(30)(111), 3.205(80)(211), 2.774(30)(220), 2.622(40)(221, 300), 2.478(40)(310), 1.960(30)(400), 1.843(30)(330, 411) (ivanyukite-Na-C); 7.85(100)(100), 3.91(20)(200), 3.201(80) (211), 2.765(20)(220), 2.602(30)(221, 300), 2.471(40)(310), 1.951(30)(400), 1.839(30)(330, 411) (ivanyukite-K); 7.87(100)(100), 3.94(20)(200), 3.205(80)(211), 2.774(20)(220), 2.616(30)(221, 300), 2.481(30)(310), 1.960(30) (400), 1.843(30)(330, 411) (ivanyukite-Cu). The crystal structure of ivanyukite-Na-T [trigonal, R3m, a = 10.921(3), c = 13.885(4) Å, V = 1434.2(7) Å3] has been solved from highly mosaic crystal and refined to R1 = 0.147 on the basis of 723 unique observed reflections. The crystal structures of ivanyukite-group minerals are based upon a 3-dimensional framework of the pharmacosiderite type, consisting of four edge-sharing TiO6-octahedra interlinked by SiO4 tetrahedra. The framework has a 3-dimensional system of channels defined by 8-membered rings with an effective channel width of 3.5 Å (calculated as the distance between O atoms across the channels minus 2.7 Å). The channels are occupied by Na+ and K+ cations and H2O molecules. The infrared spectra of the ivanyukite group minerals show 14 absorption bands caused by vibrations of Si-O and Ti-O bonds, molecular water, and (OH)- groups. Ivanyukite-Na-T formed as a late-stage, hydrothermal phase of ultra-agpaitic hydrothermalites; ivanyukite-Na-C is produced by partial hydration of ivanyukite-Na-T, and both ivanyukite-K and ivanyukite-Cu are produced by partial hydration of ivanyukite-Na-T and natural cation exchange of Cu for Na near dissolved djerfisherite and chalcopyrite grains. Nomenclature of the ivanyukite group is based on the dominant extraframework cation and symmetry of the crystal structure. The minerals are named in honor of Gregory Yur’evich Ivanyuk, Russian mineralogist and petrologist, head of the Laboratory of Self-Organized Mineral Systems in the Geological Institute of the Kola Science Centre of the Russian Academy of Sciences, for his contributions to the petrology and mineralogy of banded iron-formations, alkaline, and alkaline-ultrabasic massifs.

Whiteite-(CaMnMn), CaMnMn2Al2[PO4]4(OH)2·8H2O, a new mineral from the Hagendorf-Süd granitic pegmatite, Germany

Abstract Whiteite-(CaMnMn), CaMnMn2Al2[PO4]4(OH)2·8H2O, is a new hydrous phosphate of Ca, Mn and Al, which is closely related to both jahnsite-(CaMnMn) and the minerals of the whiteite group. It is monoclinic, P2/a, with a = 15.02(2), b = 6.95(1), c =10.13(3) Å, β = 111.6(1)º, V = 983.3(6) Å3, Z = 2 (from powder diffraction data) or a = 15.020(5), b = 6.959(2), c = 10.237(3) Å, β = 111.740(4)º, V = 984.3(5) Å3, Z = 2 (from single-crystal diffraction data). The mineral was found in the Hagendorf Süd granitic pegmatite (Germany) as small (up to 0.5 mm in size) crystals elongated on a and tabular on {010}. The crystals are either simply or polysynthetically twinned on {001}. They crystallize on the walls of voids within altered zwieselite crystals or form coronas (up to 1 mm in diameter) around cubic crystals of uraninite. The mineral is transparent, colourless to pale yellow (depending on Al-Fe3+ substitution), with a vitreous lustre and a white streak. The cleavage is perfect on {001}, the fracture is stepped and the Mohs hardness is 3½. In transmitted light, the mineral is colourless; dispersion was not observed. Whiteite-(CaMnMn) is biaxial (+), α = 1.589(2), β = 1.592(2), γ = 1.601(2) (589 nm), 2Vmeas = 60(10)º, 2Vcalc = 60.3º. The optical orientation is X = b, Z^a = 5º. The calculated and measured densities are Dcalc = 2.768 and Dmeas = 2.70(3) g cm-3, respectively. The mean chemical composition determined by electron microprobe is Na2O 0.53, MgO 0.88, Al2O3 11.66, P2O5 34.58, CaO 4.29, MnO 17.32, FeO 8.32, ZnO 2.60 wt.%, with H2O 19.50 wt.% (determined by the Penfield method), giving a total of 99.68 wt.%. The empirical formula calculated on the basis of four phosphorus atoms per formula unit, with ferric iron calculated to maintain charge balance, is (Ca0.63Zn0.26Na0.14)∑1.03(Mn0.60Fe0.402+)∑1.00(Mn1.40Fe0.372+Mg0.18Fe0.063+)∑2.01(Al1.88Fe0.123+)∑2.00[PO4]4(OH)2·7.89H2O. The simplified formula is CaMnMn2Al2[PO4]4(OH)2·8H2O. The mineral is easily soluble in 10% HCl at room temperature. The strongest X-ray powder-diffraction lines [listed as d in Å (I) (hkl)] are as follows: 9.443(65)(001), 5.596(25)(011), 4.929(80)(210), 4.719(47)(002), 3.494(46)(400), 2.7958(100)(022). The crystal structure of whiteite-(CaMnMn) was refined for a single crystal twinned on (001) to R1 = 0.068 on the basis of 5702 unique observed reflections. It is similar to the structures of other members of the whiteite group. The mineral is named for the chemical composition, in accordance with whiteitegroup nomenclature.

Chivruaiite, Ca4(Ti,Nb)5[(Si6O17)2[(OH,O)5]·13-14H2O, a new mineral from hydrothermal veins of Khibiny and Lovozero alkaline massifs

Abstract Chivruaiite is a new Ca titanosilicate [orthorhombic, Cmmm, a = 7.17(2), b = 22.98(9), c = 6.94(2) Å, V = 1144.4 Å3, 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), 2Vmeas = 40 ± 5°, 2Vcalc = 31.7°. Optical orientation: X = b, Y = a, Z = c, Dcalc = 2.42 g/cm3, Dmeas = 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 (Ca3.00K0.44 Na0.05Sr0.04Mn0.01)Σ=3.54(Ti4.13Nb0.44Fe3+0.04 Al0.02)Σ=4.63[Si12O34 |(OH)4.51O0.49]·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.

Armbrusterite, K5Na6Mn3+Mn142+[Si9O22]4(OH)10·4H2O, a new Mn hydrous heterophyllosilicate from the Khibiny alkaline massif, Kola Peninsula, Russia

Abstract Armbrusterite, ideally K5Na6Mn3+Mn2+14[Si9O22]4(OH)10·4H2O, is a new silicate of potassium, sodium, and manganese found in a thin cancrinite-aegirine-microcline vein within urtite at Mt. Kukisvumchorr. The mineral occurs in intimate association with raite. Other associated minerals are lamprophyllite, mangan-neptunite, pectolite, vinogradovite, calcite, molybdenite, galena, sphalerite, and fluorite. Armbrusterite occurs as split, curved crystals and spherulites (≤2 mm diameter). The mineral is translucent (transparent in thin fragments), dark reddish-brown. It has vitreous luster and light-brown streak. Cleavage is perfect on (001) and the fracture is uneven. Mohs hardness is about 3.5. In transmitted light, the mineral is reddish-brown, with strong pleochroism: X = light yellowish-brown, Y and Z = dark reddish-brown; dispersion r > v, weak. Armbrusterite is biaxial (.): α = 1.532(2), β = 1.560(2), γ = 1.564(2) (for λ = 589 nm), 2V varies from 10° to 20°. Optical orientation: X is perpendicular to (001). The mean chemical composition determined by electron microprobe and the Penfield method (for H2O) is (wt%): Na2O 5.26, MgO 0.19, Al2O3 0.04, SiO2 56.02, K2O 6.13, CaO 0.26, TiO2 0.04, MnO 23.62, Mn2O3 2.07, FeO 0.65, ZnO 0.20, H2O 4.1, sum. 98.58. Empirical formula calculated on the basis of Si = 36 is K5.03Na6.55(Mn2+12.86Mn3+1.01Fe2+0.35Mg0.18 Ca0.18Zn0.09Al0.03Ti0.02)Σ=14.72[Si36O88](OH)10.10 ·3.75 H2O. Armbrusterite is monoclinic, C2/m, a = 17.333(2), b = 23.539(3), c = 13.4895(17) Å, β = 115.069(9)°, V = 4985.4(11) Å3, Z = 2. The strongest X-ray powder-diffraction lines are [d in Å, (I), (hkl)]: 12.28 (100) (001), 4.10 (10) (003), 3.562 (10) (113, 261), 3.260 (18) (114), 3.117 (13) (203), 3.077 (54) (004), 2.622 (10) (371). The crystal structure of armbrusterite was refined to R1 = 0.085 on the basis of 3960 unique observed reflections. The structure is based upon double silicate [Si9O22] layers consisting of 5-, 6-, 7-, and 8-membered tetrahedra rings. The layers are linked via octahedral sheets formed by Na and Mn octahedra. The interior of the double silicate layers is occupied by K+ cations and H2O molecules. The mineral is named in honor of Thomas Armbruster (b. 1950; University of Berne) for his outstanding contribution to structural mineralogy and crystallography, especially to the study of Mn-rich minerals.

Rock-Forming feldspars of the Khibiny alkaline pluton, Kola Peninsula, Russia

This paper describes the structural-compositional zoning of the well-known Khibiny pluton in regard to rock-forming feldspars. The content of K-Na-feldspars increases inward and outward from the Main foidolite ring. The degree of coorientation of tabular K-Na-feldspar crystals sharply increases in the Main ring zone, and microcline-dominant foyaite turns into orthoclase-dominant foyaite. The composition of K-Na-feldspars in the center of the pluton and the Main ring zone is characterized by an enrichment in Al. This shift is compensated by a substitution of some K and Na with Ba (the Main ring zone) or by an addition of K and Na cations to the initially cation-deficient microcline (the central part of the pluton). Feldspars of volcanosedimentary rocks occurring as xenoliths in foyaite primarily corresponded to plagioclase An15–40, but high-temperature fenitization and formation of hornfels in the Main ring zone gave rise to the crystallization of anorthoclase subsequently transformed into orthoclase and albite due to cooling and further fenitization. Such a zoning is the result of filling the Main ring fault zone within the homogeneous foyaite pluton with a foidolite melt, which provided the heating and potassium metasomatism of foyaite and xenoliths of volcanosedimentary rocks therein. The process eventually led to the transformation of foyaite into rischorrite-lyavochorrite, while xenoliths were transformed into aluminum hornfels with anorthoclase, annite, andalusite, topaz, and sekaninaite.

Polezhaevaite-(Ce), NaSrCeF6, a new mineral from the Khibiny massif (Kola Peninsula, Russia)

Abstract Polezhaevaite-(Ce) NaSrCeF6 is a new member of the gagarinite mineral group [hexagonal, P63/m, a = 6.207(7) Å, c = 3.801(9) Å, V = 126.8(2) Å3, Z = 1]. It is found in a natrolitized microcline-aegirinesodalite lens within apatite-rich urtite at Mt. Koashva (Khibiny massif, Kola Peninsula, Russia) in association with аegirine, albite, arfvedsonite, astrophyllite, burbankite, catapleiite, chlorbartonite, djerfisherite, elpasolite, fluorapatite, fluorite, galena, hydroxylapatite, ilmenite, lamprophyllite, lorenzenite, leucophanite, microcline, natrolite, nepheline, orickite, pectolite, pyrochlore, sodalite, sphalerite, strontiofluorite, tainiolite, titanite, vinogradovite, and villiaumite. Polezhaevaite-(Ce) occurs as parallel and sheaf-like aggregates of extremely thin fibers (up to 1 mm long and <1 μm thick), which fill leaching voids within burbankite crystals in natrolite and mantles around partially dissolved burbankite crystals in intimate association with strontiofluorite. Polezhaevaite-(Ce) is translucent (transparent in separate fibers), snowy-white, with a silky luster (in aggregates) and a white streak. Cleavage is not observed; fracture is splintery (in aggregates). The Mohs hardness of individual crystals could not be determined and approaches 3 in aggregates. In transmitted light, the mineral is colorless, uniaxial positive: ε = 1.497(5), ω = 1.490(5) (for λ = 589 nm). Dcalc = 4.646 g/cm3, Dmeas = >4.2 g/cm-3. The mean chemical composition determined by electron microprobe is (wt%): Na 5.27, Ca 3.08, Sr 29.72, Ba 0.48, La 11.76, Ce 14.12, Pr 0.49, Nd 3.09, F 31.95, total 99.96. Empirical formula calculated on the basis of F = 6 apfu is: (Na0.82Ca0.18)Σ=1.00(Sr1.21Ce0.36La0.30Ca0.09Nd0.08Ba0.01)Σ=2.06F6 (charge imbalance is +0.05). Its simplified formula is NaSrCeF6. The strongest X-ray powder-diffraction lines [d in Å, (I), (hkl)] are: 5.416(40)(100), 3.120(100)(101, 110), 2.198(70) (201), 1.796(90)(121, 211, 300, 102), 1.554(30)(220), 1.173(70)(321, 231, 140, 410,132, 312, 113). The mineral is named in honor of Lyudmila Ivanovna Polezhaeva (b. 1935), a Russian expert in electron microprobe analysis of minerals for her contribution to the mineralogy of alkaline rocks

First Natural Pharmacosiderite-Related Titanosilicates and Their Ion-Exchange Properties

In 1990, Chapman and Roe prepared a number of titanosilicate analogues of pharmacosiderite, including Cs, Rb and exchanged protonated phases. Harrison et al. (1995) reported structure of Cs3H[Ti4O4(SiO4)3](H2O)4. Behrens et al. (1996), Behrens and Clearfield (1997) and Dadachov and Harrison (1997) provided data on preparation, structures and properties of A 3H[Ti4O4(SiO4)3](H2O) n (A = H, Na, K, Cs). Structures and ion-exchanged properties of HA 3[M 4O4(XO4)3](H2O)4 (A = K, Rb, Cs; M = Ti, Ge; X = Si, Ge) were reported by Behrens et al. (1998). These compounds were considered as perspective materials for the selective removal of Cs and Sr from wastewater solutions. However, no natural titanosilicates with pharmacosiderite topology have been reported so far. In this article, we report for the first time occurrence of four pharmacosiderite-type titanosilicates in Nature and their cation-exchange properties.

Minerals of the gadolinite-(Y)-hingganite-(Y) series in the alkali granite pegmatites of the Kola Peninsula

Minerals of the gadolinite-(Y)-hingganite-(Y) series pertaining to the gadolinite-datolite group have been found in the alkali granite pegmatites of the Kola Peninsula. Gadolinite-(Y) is distinguished by its unique natural crystalline state. The unit-cell parameters of this mineral have elevated values as compared with those of gadolinite-(Y) from other deposits and occurrences: (i) a = 10.11 Å, b = 7.63 Å, c = 4.79, V = 369.30 Å3; (ii) a = 10.05 Å, b = 7.69 Å, c = 4.76, V = 367.99 Å3. The increase in unit-cell parameters is not correlated with variation in chemical composition. The variable chemical compositions of particular individuals, especially as concerns REE and Y contents, assume two gadolinite-(Y) generations being contained in the intragranite pegmatites. Gadolinite-I is characterized by a high LREE content (LREEN/HREEN = 1.6) with a prevalence of total REE over Y (REE/Y = 1.36). Gadolinite-II is significantly depleted in LREE (LREEN/HREEN = 0.3) with a prevalence of Y over REE (REE/Y = 0.29). Hingganite-(Y), which has also been found in the alkali granite pegmatites of the Kola Peninsula for the first time, is characterized by elevated unit-cell parameters as well: a = 10.05 Å, b = 7.72 Å, c = 4.76 Å, V = 369.12 Å3. The mineral is enriched in Ca (up to 5 wt % CaO); and, by contents of REE and Y, the hingganite-(Y) from inter-granite pegmatites keeps the marginal position between its Y-dominant and REE-dominant varieties. The chondrite-normalized REE patterns assume that hingganite-(Y) crystallizes between the first and the second generations of gadolinite-(Y) and that alkali intragranite pegmatites are formed at the late magmatic stage, whereas amazonite-bearing pegmatites are formed under postmagmatic hydrothermal conditions.

Fluorbritholite(Y) and Yttrialite(Y) from Silexites of the Keivy Alkali Granites, Kola Peninsula

Investigation of the morphology, anatomy, and chemical composition of fluorbritholite-(Y) and yttrialite-(Y) from silexites of the Keivy alkali granites in Kola Peninsula has shown that these minerals are the main REE concentrators in this area and that their content reaches 10–15 vol %. Britholite and yttrialite are associated with zircon, aeschynite-(Y), chevkinite-(Ce), fergusonite-(Y), thorite, monazite-(Ce), xenotime-(Y) and bastnaesite-(Ce). Three morphological types of fluorbritholite-(Y) have been identified: (I) subhedral crystals and grains, (II) anhedral grains intergrown with yttrialite-(Y), and (III) poikilitic crystals and skeletal aggregates. These morphological types of fluorbritholite-(Y) are characterized by successive (I to III type) decreases in P content down to the pure silicate fluorbritholite-(Y). Crystals of the first type are heterogenous: the P content decreases and the HREE content increases from core to rim. The total REE content increases insignificantly from types I to II and drastically decreases in fluorbritholite-(Y) of type III. The successive prevalence of HREE over LREE indicates the hydrothermal conditions of mineral crystallization. The chemical composition of yttrialite-(Y) is distinguished by the relatively high Th content and depletion in Al. The compositional trend (from core to rim) in heterogeneous grains of yttrialite-(Y) testifies that their heterogeneity was caused by metasomatic alteration of the mineral. The interrelation of fluorbritholite-(Y) and yttrialite-(Y) indicate that fluorbritholite-(Y) of types II and III were formed later than yttrialite-(Y). Evidence for fluorbritholite-(Y) and yttrialite-(Y) formation suggests the significant role of hydrothermal processes in the genesis of silexites.

Behoite and Mimetite from the Saharjok Alkaline Intrusion, Kola Peninsula

The detailed study of the mineral composition of the nepheline syenite pegmatite from the Saharjok Intrusion has resulted in the finding of behoite and mimetite, a mineral species identified in the Kola region for the first time. The pegmatite body at the contact between nepheline syenite and essexite is unusual in textural and structural features and combination of mineral assemblages including unique beryllium mineralization. Behoite Be(OH)2 is an extremely rare beryllium mineral. It occurs as powderlike aggregates in the leaching cavities between euhedral pyroxene crystals. Behoite was identified by comparison of X-ray powder diffraction data of the studied mineral phase and behoite from the Be-bearing tuff in the type locality of this mineral (Utah, United States). Mimetite was found in the same pegmatite of the Saharjok intrusion. It forms unusual parallel-fibrous aggregates with individual fibers as long as ∼1 mm and only ∼1 μm across. X-ray powder diffraction data and the chemical composition characterize the mineral as hexagonal phase Pb5[AsO4]3Cl. Both behoite and mimetite are the products of late hydrothermal alteration of primary minerals (meliphanite, galena, arsenopyrite, and loellingite). The secondary phases freely crystallized in the cavities remaining after the leached nepheline.