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Kirovsk, Russia

Yakovenchuk V.N.,Russian Academy of Sciences | Ivanyuk G.Y.U.,Russian Academy of Sciences | Pakhomovsky Y.A.,Russian Academy of Sciences | Selivanova E.A.,Russian Academy of Sciences | And 2 more authors.
Canadian Mineralogist | Year: 2010

Strontiofluorite, SrF2, is a new member of the fluorite group [cubic, Fm3̄m, a 5.713(8) Å, Z = 4]. It occurs in a "natrolitized" sodalite - microcline - aegirine lens within apatite-rich urtite at Mt. Koashva in the Khibiny alkaline complex. Kola Peninsula, Russia. The new mineral species is associated with astrophyllite, burbankite, chlorbartonite, fluorapatite, fluorite, lamprophyllite, polezhaevaite-(Ce) and villiaumite. Strontiofluorite occurs as cubo-octahedral crystals (up to 0.5 mm in diameter) and compact masses that cement fibrous aggregates of polezhaevaite-(Ce) in voids caused by leaching of burbankite crystals. Also, strontiofluorite occurs in fine-grained orthoclase-bearing urtite at Mt. Kitchepakhk, also in the Khibiny complex, where it forms lenticular inclusions up to 0.2 mm in length in natrolite and albite associated with orthoclase, nepheline, ferrorichterite, aegirine, lamprophyllite, lorenzenite, stronadelphite and an as-yet unnamed phase of composition Sr 2PO4F. Strontiofluorite is translucent, pale grey, with a greasy luster and a white streak. Cleavage is perfect on {111}, and the fracture is step-like. The Mohs hardness is 4. In transmitted light, the mineral is colorless, isotropic; n = 1.438(2) (for λ= 589 nm). The calculated density is 4.11 g cm-3, and the measured density is 4.05 g cm -3. The mean chemical composition of the Koashva sample, determined with an electron microprobe, is (wt.%): Na 1.79, Ca 9.57, Sr 42.81, Ba 7.06, La 2.14, Ce 2.78, Nd 0.64, F 33.15, total 99.94. The empirical formulae calculated on the basis of two atoms of F are: (Sr0.56Ca0.27Na 0.09Ba0.06Ce0.02La0.02Nd 0.01) Σ1.03 F2 (Koashva) and (Sr 0.88Ca0.08Na0.02Fe2+0.02 Ba0.01Mn0.01)Σ1.02F2 (Kitchepakhk), which gives a charge imbalance of +0.02. The simplified formula is SrF2.The strongest lines in the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 3.32(100)(111), 2.886(20)(200), 2.029(90)(220), 1.731 (60)(311 ), 1.317(30)(331 ) and 1.172(50)(422). The mineral is named as a Sr-dominant analogue of fluorite. Source

Yakovenchuk V.N.,Russian Academy of Sciences | Selivanova E.A.,Russian Academy of Sciences | Ivanynyuk G.Yu.,Russian Academy of Sciences | Pakhomovsvsky Y.A.,Russian Academy of Sciences | And 2 more authors.
American Mineralogist | Year: 2010

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-aegirine-sodalite lens within apatite-rich urtite at Mt. Koashva (Khibiny massif, Kola Peninsula, Russia) in association with ?egirine, 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: (Na0.82Ca 0.18)∑=1.00(Sr1.21Ce0.36La 0.30Ca0.09 Nd0.08Ba0.01) ∑=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. Source

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