Fluorbritholite-(Y), (Y,Ca,Ln)5[(Si,P)O4]3 F, a new mineral of the britholite group
Pekov, Igor V.; Zubkova, Natalia V.; Chukanov, Nikita V.; Husdal, Tomas A.; Zadov, Aleksandr E.; Pushcharovsky, Dmitry Y.u.
published: Apr 1, 2011
ArtNo. ESP154018802008, Price: 29.00 €
The new britholite-group mineral fluorbritholite-(Y) was found in pegmatites related to alkaline granites. In Hamarøy, Nordland, Norway, it occurs in Lagmannsvik [the holotype, grains up to 1 mm with Y-rich fluorite, allanite-(Ce), quartz, bastnäsite-(Ce), britholite-(Y), gadolinite-(Y), hundholmenite-(Y), etc.] and Kråkmo [rims around fluorapatite, with quartz, fluorite, allanite-(Ce), britholite-(Y), fluorcalciobritholite and tengerite-(Y)]. At Mt. Vyuntspakhk, Western Keivy, Kola Peninsula, Russia, the mineral forms coarse, hexagonal, prismatic to tabular crystals and irregular grains up to 2.5 × 4 cm, with quartz, magnetite, microcline, zircon, fergusonite-(Y) and thorite. Fluorbritholite-(Y) is transparent, from light pinkish-brown to dark brown. Mohs' hardness is 5.5, no cleavage was observed, fracture is uneven to conchoidal. Dcalc. for the holotype is 4.61 g/cm3. Optically, it is uniaxial (+), ω 1.784(2), ε 1.789(3). The IR spectrum is given. Average values for four point microprobe analyses of the holotype are (wt.%): CaO 12.21, MnO 1.06, Y2O3 30.80, La2O3 1.13, Ce2O3 7.12, Pr2O3 0.69, Nd2O3 6.85, Sm2O3 2.15, Gd2O3 2.23, Dy2O3 2.80, Er2O3 2.61, Yb2O3 3.75, SiO2 24.18, P2O5 0.29, F 2.01, - O = F2 −0.85; total 99.03. The empirical formula based on 13 anions is: [(Y2.013Ce0.320Nd0.300Yb0.140Dy0.111Er0.101Gd0.091Sm0.091La0.051Pr0.031)Σ3.249Ca1.607Mn0.110]Σ4.966 [(Si2.970P0.030)Σ3O12][F0.781O0.210(OH)0.009]Σ1. The simplified formula is: (Y,Ca,Ln)5[(Si,P)O4]3 F. The crystal structure was refined to R = 4.46 % from single-crystal X-ray diffraction data. Fluorbritholite-(Y) is hexagonal, P63/m; a = 9.4437(2), c = 6.8169(2) Å, V = 526.50(2) Å3, Z = 2. It is isostructural with fluorapatite. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 4.104 (27) (200), 3.160 (27) (102), 3.102 (29) (210), 2.826 (100) (121), 2.775 (58) (112), 2.737 (46) (300), 1.948 (25) (222), 1.839 (28) (123). The mineral is named as the fluorine-dominant analogue of britholite-(Y). The type specimen is deposited in the Fersman Mineralogical Museum, Moscow.