Hingganite-(Ce) and hingganite-(Y) from Tahara, Hirukawa-mura, Gifu Prefecture, Japan: The description on a new mineral species of the Ce-analogue of hingganite-(Y) with a refinement of the crystal structure of hingganite-(Y)

Abstract

Hingganite-(Ce), Ce₂[]Be₂Si₂O₈(OH)₂ or CeBeSiO₄(OH), occurs in a pegmatite at Hirukawa-mura, Gifu Prefecture, Japan. It is pale tan in color, vitreous and transparent, with a white streak. The Mohs hardness is 5-6, and the calculated density is 4.28 g/cm³. An electron microprobe analysis gave the empirical formula (Ce_0.82La_0.32Nd_0.13Pr_0.06Y_0.03Sm_0.01 Gd_0.002Dy_0.001Ca_0.60)Σ_1.97Fe_0.24Be_2.02Si_2.02O_8.20(OH)_1.52. The lattice parameters were determined by the Rietveld method coupled with the imaging plate Gandolfi XRD data: SG = P2₁/a, a = 9.8973(11), b = 7.6282(8), c = 4.7505(6) Å, β = 90.416(8)°, V = 358.64(7) ų, and Z = 2 for Ce₂[]Be₂Si₂O₈(OH)₂. The three strongest lines in the powder XRD pattern [d(Å), I/I₀, hkl] are (3.14, 86, 211 and 211), (2.85, 100, 121 and 121) and (2.56, 46, 311, 221 and 311). Hingganite-(Ce) is a new member of the gadolinite-datolite group of minerals. It is the Ce-analogue of hingganite-(Y), and ideally, is the Fe-free analogue of gadolinite-(Ce). A single crystal of hingganite-(Y) from the same locality showed a chemical composition of (Y_1.21Ca_0.28Nd_0.06Gd_0.06Dy_0.06Yb_0.05Er_0.04Ce_0.04Sm_0.03Ho_0.03Lu_0.02Pr_0.01Tm_0.01Tb_0.01La_0.01)Σ_1.92Fe_0.23Be_2.07Si_2.07O_8.19(OH)_1.55. A negative anomaly was observed for Ho in the lanthanide distribution pattern of hingganite-(Y). A single crystal structure refinement of hingganite-(Y) converged to R = 0.0329 with the lattice parameters of: a = 9.8830(16), b = 7.6091(9), c = 4.7423(9) Å, β = 90.342(14)°, and V = 356.62(10) ų.