Taipingite-(Ce), (Ce73+, Ca2)Σ9Mg(SiO4)3[SiO3(OH)]4F3, a new mineral from the Taipingzhen REE deposit,North Qinling Orogen,central China |
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| Institution: | 1. Tianjin Center, China Geological Survey, Tianjin 300170, China;2. Beijing Research Institute of Uranium Geology, Beijing 100029, China;3. China University of Geosciences(Beijing), Beijing 100083, China;4. Chengdu Center, China Geological Survey, Chengdu 610081, China;5. Henan Nuclear Geological Bureau, Zhengzhou 450044, China |
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| Abstract: | A new cerite group mineral species, taipingite-(Ce), ideally (Ce73+, Ca2)Σ9Mg(SiO4)3SiO3(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)]3.98PO3(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). |
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| Keywords: | Taipingite-(Ce) Cerite group New mineral species Chemical composition Crystal structure North Qinling Orogen |
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