Taipingite-(Ce), (Ce73+, Ca2)Σ9Mg(SiO4)3[SiO3(OH)]4F3, a new mineral from the Taipingzhen REE deposit, North Qinling Orogen, central China

• Published in: Di xue qian yuan. Vol. 11; no. 6; pp. 2339 - 2346
• Main Authors: Qu, Kai, Sima, Xianzhang, Fan, Guang, Li, Guowu, Shen, Ganfu, Chen, Huakai, Liu, Xing, Yin, Qingqing, Li, Ting, Wang, Yanjuan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2020; Tianjin Center, China Geological Survey, Tianjin 300170, China%Beijing Research Institute of Uranium Geology, Beijing 100029, China%China University of Geosciences(Beijing), Beijing 100083, China%Chengdu Center, China Geological Survey, Chengdu 610081, China%Henan Nuclear Geological Bureau, Zhengzhou 450044, China
• Subjects: Cerite group; Chemical composition; Crystal structure; New mineral species; North Qinling Orogen; Taipingite-(Ce); Cerite group; North Qinling Orogen; Chemical composition; New mineral species; Taipingite-(Ce); Crystal structure
• ISSN: 1674-9871
• DOI: 10.1016/j.gsf.2020.02.006

A new cerite group mineral species, taipingite-(Ce), ideally (Ce73+, Ca2)Σ9Mg(SiO4)3[SiO3(OH)]4F3, has been found in the Taipingzhen rare earth element (REE) deposit in the North Qinling Orogen (NQO), Central China. It forms subhedral grains (up to approximately 100 ​μm ​× ​200 ​μm) commonly intergrown with the REE mineral assemblages and is closely associated with allanite-(Ce), gatelite-(Ce), törnebohmite-(Ce), fluocerite-(Ce), fluocerite-(La), fluorite, bastnäsite-(Ce), parisite-(Ce) and calcite. Taipingite-(Ce) is light red to pinkish brown under a binocular microscope and pale brown to colorless in thin section, and it is translucent to transparent with a grayish-white streak and vitreous luster. This mineral is brittle with conchoidal fracture; has a Mohs hardness value of approximately 5½ and exhibits no cleavage twinning or parting. The calculated density is 4.900(5) g/cm3. Optically, taipingite-(Ce) is uniaxial (+), with ω ​= ​1.808(5), ε ​= ​1.812(7), c ​= ​ε, and a ​= ​b ​= ​ω. Furthermore, this mineral is insoluble in HCl, HNO3 and H2SO4. Electron microprobe analysis demonstrated that the sample was relatively pure, yielding the empirical formula (with calculated H2O): (Ce4.02La1.64Nd1.49Pr0.41Sm0.10Gd0.02Ho0.02Tm0.01Lu0.02Y0.03Ca0.66Mg0.05Th0.01–0.51)Σ9(Mg0.75Fe0.253+)Σ1(SiO4)3{[SiO3(OH)]3.98[PO3(OH)]0.02}Σ4(F1.81OH1.17Cl0.02)Σ3. Taipingite-(Ce) is trigonal and exhibits space group symmetry R3c with unit cell parameters a ​= ​10.7246(3) Å, c ​= ​37.9528(14) Å, V ​= ​3780.39(20) Å3 and Z ​= ​6. The strongest eight lines in the X-ray diffraction pattern are [d in Å(I)(hkl)]: 4.518(50)(202), 3.455(95)(122), 3.297(85)(214), 3.098(35)(300), 2.941(100)(02,10), 2.683(65)(220), 1.945(40)(238) and 1.754(40)(30,18). The crystal structure has been refined to a R1 factor of 0.025, calculated for the 2312 unique observed reflections (Fo ​≥ ​4σ). The mineral is named after its discovery locality and is characterized as the F-dominant analogue of cerite-(Ce). [Display omitted] •A new cerite group mineral—taipingite-(Ce) has been found in the North Qinling Orogen (NQO), Central China.•The ideal formula of taipingite-(Ce) is (Ce73+Ca2)Σ9Mg(SiO4)3[SiO3(OH)]4F3.•Taipingite-(Ce) is trigonal, space group ​R3c, with ​a ​= 10.7246(3) Å, ​c ​= 37.9528(14) Å, ​V ​= 3780.39(20) Å3.