The new mineral stetindite, CeSiO_4, a cerium end-member of the zircon group

摘要

The new mineral stetindite (IMA-CNMNC No. 2008-035) has the ideal chemical formula CeSiO_4. It is tetragonal with space group I4_1/amd. Unit-cell data from single-crystal X-ray studies gave a = 6.9746(7), c = 6.2055(8) (A), V = 301.87(7) A~3 , Z = 4. Stetindite is the Ce~(4+)-dominant analogue of zircon (ZrSiO_4) and hafnon (HfSiO_4). The strongest reflections in the X-ray powder diffraction data are as follows d_(obs) (A) (I, hkl): 3.478 (100, 200), 1.789 (39, 312), 4.616 (30, 101) and 2.617 (30, 112). Stetindite was found in the Stetind pegmatite, Tysfjord, 135 km NE of Bod0, northern Norway. It occurs as pale yellow to colourless crystals mostly as diverging aggregates of acicular crystals which reach a length of 1.5 mm and a thickness of 0.05 mm. The calculated density is 5.03 g/cm~3. The mineral is optically uniaxial positive with a calculated main refractive index of 2.01. Stetindite is found in vugs of yttrian fluorite masses and is closely associated with hematite, hundholmenite-(Y), quartz, tornebohmite-(Ce), vyuntspakhkite-(Y), calcioancylite-(Nd), Kozoite-(Nd), Nd-rich bastnasite and a new Ca-Y-Al-F-silicate. Chemical analyses gave (wt.%): CeO_2 65.17, Y_2O_3 6.35, Gd_2O_3 1.32, SiO_2 25.94, F 0.69, O = F -0.29, sum 99.18 wt.%. The resulting empirical formula based on 4 anions is (Ce_(0.87),Y_(0.13),Gd_(0.02))Si_(1.00)O_(3.92)F_(0.08).