Abstract
Polezhaevaite-(Ce) NaSrCeF6 is a new member of the gagarinite mineral group [hexagonal, P 63/ m , a = 6.207(7) A, c = 3.801(9) A, V = 126.8(2) A3, 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 aegirine, 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 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)∑=1.00(Sr1.21Ce0.36La0.30Ca0.09 Nd0.08Ba0.01)∑=2.06F6 (charge imbalance is +0.05). Its simplified formula is NaSrCeF6. The strongest X-ray powder-diffraction lines [ d in A, ( 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.
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