著者

Hidemichi HORI Toshinori Kobayashi Ritsuro MIYAWAKI Satoshi MATSUBARA Kazumi YOKOYAMA Masaaki SHIMIZU

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.101, no.4, pp.170-177, 2006 (Released:2006-08-08)

参考文献数

23

被引用文献数

4 8

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Iwashiroite-(Y), YTaO4, was found from Suishoyama, Kawamata Town, Fukushima Prefecture, Japan. It is monoclinic, P2/a, a = 5.262(5) Å, b = 5.451(5) Å, c = 5.110(5) Å, β = 95.12(10)°, V = 146.0(2) Å3, Z = 2. The five strongest lines in the powder XRD pattern [d(Å), I/I0, hkl] are (3.13, 100, 111), (2.95, 94, 111), (2.73, 26, 020), (1.890, 29, 220) and (1.862, 29, 022). Electron microprobe analysis gave; Y2O3 29.10, Ce2O3 0.10, Nd2O3 0.10, Sm2O3 0.36, Gd2O3 1.06, Tb2O3 0.25, Dy2O3 2.38, Ho2O3 0.56, Er2O3 2.09, Tm2O3 0.37, Yb2O3 3.33, Lu2O3 0.85, ThO2 0.02, UO2 0.15, CaO 0.17, Ta2O5 40.64, Nb2O5 16.66, TiO2 0.41, total 98.60 wt%, and leads to the empirical formula, (Y0.81Yb0.05Dy0.04Er0.03Gd0.02Lu0.01Ho0.01Sm0.01Ca0.01Tm0.01)Σ1.00(Ta0.58Nb0.39Ti0.02)Σ0.99O4 on the basis of the 4 oxygen atoms per formula unit. Iwashiroite-(Y) is translucent and amber brown to brown in color with a glassy to subadamantine luster. The streak is pale brown and cleavage is {010} good, {001} poor. The Mohs' hardness is 6. The calculated density is 7.1 g/cm3. Iwashiroite-(Y) occurs as an aggregate of small euhedral platy crystals with a metamict substance in the main ore body of the granite pegmatite mine at the locality. Associated minerals are quartz, microcline and annite. The crystal structure was refined to R = 0.034 with single crystal XRD data. Although the structure consists of TaO6 octahedra and YO8 polyhedra, iwashiroite-(Y) is not isostructural with fergusonite-beta-(Y).