著者

Daisuke NISHIO–HAMANE Koichi MOMMA Masayuki OHNISHI Sachio INABA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.117, no.1, pp.220728, 2022 (Released:2022-11-29)

参考文献数

24

被引用文献数

1

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Oxyyttrobetafite–(Y) is the first member in the betafite group of the pyrochlore supergroup found in albite–rich pegmatite from Souri Valley, Komono, Mie Prefecture, Japan. This new mineral occurs as small anhedral grains with sizes of 20 to 200 µm in cylinder–shaped aggregates with a substrate of thalénite–(Y) and synchysite–(Y). Small amounts of aeschynite–(Y), thorianite, and thorite are also associated in the same occurrence with oxyyttrobetafite–(Y), and gadolinite–(Y) is also included at the boundary between the aggregate and albite. The physical properties are: brown in color, brittle, transparent, non–fluorescent, vitreous luster, white streak with a Mohs hardness of 5, and a calculated density of 5.54 g·cm−3. Oxyyttrobetafite–(Y) is an optically isometric material with brown color under the microscope with a refractive index of n = 2.3 calculated using the Gladstone–Dale relationship. The empirical formula of oxyyttrobetafite–(Y) calculated on the basis of B = 2 with A2B2X6Y composition is (Y1.58Dy0.13Yb0.07Er0.06Tm0.05Gd0.04Ho0.03Sm0.02Tb0.02Eu0.01Lu0.01)Σ2.02(Ti1.85Ta0.09Fe0.05Sn0.02Nb<0.01)Σ2O7.05 and leads to the ideal formula of Y2Ti2O6O, which requires TiO2 41.44 wt% and Y2O3 58.56 wt%, total 100 wt%. The structure is isometric cubic with the space group Fd3m and unit cell parameters of a = 10.11090(10) Å, V = 1033.64(3) Å3, and Z = 8 by single crystal X–ray diffraction measurements. The seven strongest peaks in the powder X–ray diffraction pattern [d in Å (I/I0) hkl ] were 2.918(100) 222, 2.527(18) 400, 2.321(13) 331, 1.788(53) 440, 1.525(46) 622, 1.162(13) 662, and 1.033(9) 844 with unit cell parameters of a = 10.121(3) Å, V = 1036.6(9) Å3, and Z = 8. The crystal structure was refined to R1 = 0.018 for 159 observed reflections with the criteria of I > 2σ (I ). Oxyyttrobetafite–(Y) is characterized by Y dominance at the A sites, Ti dominance at the B sites, and O dominance at the X and Y sites in the A2B2X6Y pyrochlore–type formula.

著者

Daisuke NISHIO–HAMANE Masayuki OHNISHI Norimasa SHIMOBAYASHI Koichi MOMMA Ritsuro MIYAWAKI Sachio INABA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.115, no.3, pp.286-295, 2020 (Released:2020-06-24)

参考文献数

30

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Petersite–(La) is a new mineral of the petersite series in the mixite group with an ideal formula of Cu6La(PO4)3(OH)6·3H2O from Ohgurusu, Kiwa–cho, Kumano City, Mie Prefecture, Japan. The mixite–group minerals occur in small cavities coated by chrysocolla developed along quartz veins. Four members from different cavities have been identified: petersite–(La), petersite–(Ce), petersite–(Y), and agardite–(La). Petersite–(La) occurs as a radial aggregate formed by acicular to hexagonal columnar crystals of yellowish green color. Crystals are elongated along [001] and the prismatic face is probably formed by {001} and {100} or {110}. It is non–fluorescent in UV light. Crystals are brittle, cleavage and parting are non–observed, and fracture is uneven. These characteristics are common in other mixite–group minerals. The calculated density of petersite–(La) is 3.33 g/cm3, based on the empirical formula and powder XRD data. It is optically uniaxial positive with ω = 1.680(3) and ε = 1.767(3) (white light), and pleochroism varies from light green to yellowish green. Based on the WDS analysis, the empirical formula of petersite–(La) calculated on the basis of P + As + Si = 3 is (Cu5.692Fe0.010)Σ5.702[(La0.148Ce0.122Nd0.117Y0.086Sm0.022)Σ0.495Ca0.372]Σ0.866(P1.890As0.799Si0.311)Σ3O10.320(OH)7.680·3H2O. Petersite–(La) is hexagonal (P63/m) with a = 13.367(2) Å, c = 5.872(2) Å, and V = 908.7(4) Å3 (Z = 2). The eight strongest lines of petersite–(La) in the powder XRD pattern [d in Å(I/I0)(hkl )] are 11.578(100)(100), 4.377(28)(210 + 120), 3.509(18)(211 + 121), 3.211(10)(310 + 130), 2.898(14)(221, 400), 2.656(10)(320 + 230), 2.526(11)(410 + 140), and 2.438(25)(212 + 122). Petersite–(La) is the third defined member in the petersite series and corresponds to the La–dominant analogue of petersite–(Y) and petersite–(Ce).