Dingdaohengite-(Ce) from the Bayan Obo REE-Nb-Fe Mine, China: Both a true polymorph of perrierite-(Ce) and a titanic analog at the C1 site of chevkinite subgroup
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Jinsha Xu
,
Guaming Yang
Abstract
Dingdaohengite-(Ce), ideally Ce4Fe2+Ti2Ti2(Si2O7)2O8, is a new member of the chevkinite group minerals from the world-famous Bayan Obo REE-Nb-Fe Mine near Baotou city, Inner Mongolian Autonomous Region, North China. It occurs in the magnesian skarn in the excontact of granite within dolomitic marble. Most individual crystals vary from 0.2 to 1.0 cm in length. Associated minerals are diopside, tremolite, richterite, allanite-(Ce), magnetite, ilmenite, spinel, titanite, pyrochlore, F-rich phlogopite, fluorapatite, quartz, and fluorite, etc. Dingdaohengite-(Ce) is probably of bimetasomatic origin among Ca-Mg-carbonate rock and/or carbonatite, and REE-, F-rich postmagmatic hydrothermal solutions. The mineral is black and becoming brown black in thin fragments. It is translucent to opaque with a submetallic-metallic luster, and a brown streak. It is brittle with conchoidal fracture. No cleavage or parting is observed. Its hardness is VHN25g 606.0-717.4 kg/mm2 (Mohs hardness near 5.9). The measured density is 4.83(7) g/cm3 and the calculated density is 4.88(0) g/cm3. Its reflectance values (for λ = 589 nm) are 11.4-12.5%. It is biaxial negative. The strongest six X-ray diffraction lines in the powder pattern [d in Å (I) (hkl)] are 2.7524(100)(121), 2.7263(98)(313), 3.1978(68)(212), 2.5460(54)(304), 2.8702(52)(020), and 3.1622(46)(312).
An electron-microprobe analysis on the crystal used to collect X-ray intensity data for crystalstructure refinement gives SiO2 19.29, TiO2 18.26, Al2O3 0.04, FeO 8.49, Fe2O3 1.67, ThO2 0.16, MgO 1.32, CaO 2.17, Nb2O5 0.47, Ta2O5 0.00, La2O3 19.53, Ce2O3 28.08, Nd2O3 n.d., Y2O3 0.00, Na2O 0.00, sum 99.48 wt%; the Fe3+ /Fe2+ ratio was converted by Mössbauer spectroscopy. The empirical formula is (Ce2.13La1.49Ca0.48Th0.01)Σ4.11Fe2+(Ti0.88Fe2+0.47Mg0.41Fe3+0.26Al0.01)Σ2.03(Ti1.96Nb0.04)Σ2.00(Si2O7)2O8, based on 22 O atoms with prevalence of Ti in the C1 site of the structure. Dingdaohengite-(Ce) is monoclinic, a = 13.4656(15) Å, b = 5.7356(6) Å, c = 11.0977(12) Å, β = 100.636(2)°, V = 842.39(46) Å3, and Z = 2. The crystal structure of dingdaohengite-(Ce) was refined with space groups P21/a and C2/m. Pseudo-extinction was found, i.e., reflections with h + k = 2n are systematically strong, while those with h + k = 2n + 1 are weak, which show that the true space group of dingdaohengite-(Ce) is P21/a (pseudo-C2/m).
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- The crystal structure of vurroite, Pb20Sn2(Bi,As)22S54Cl6: OD-character, polytypism, twinning, and modular description
- Mineralogy of the Paso Robles soils on Mars
- Dingdaohengite-(Ce) from the Bayan Obo REE-Nb-Fe Mine, China: Both a true polymorph of perrierite-(Ce) and a titanic analog at the C1 site of chevkinite subgroup
- Thermal equation of state of CaGeO3 perovskite
- Quantitative absorbance spectroscopy with unpolarized light: Part I. Physical and mathematical development
- Quantitative absorbance spectroscopy with unpolarized light: Part II. Experimental evaluation and development of a protocol for quantitative analysis of mineral IR spectra
- Oxide-melt solution calorimetry of selenides: Enthalpy of formation of zinc, cadmium, and lead selenide
- Precise dating of biotite in distal volcanic ash: Isolating subtle alteration using 40Ar/39Ar laser incremental heating and electron microprobe techniques
- Rationale for the existence of four- and eight-reversals in antigorite
- Structural relaxation around substitutional Cr3+ in pyrope garnet
- Metasomatic thorite and uraninite inclusions in xenotime and monazite from granitic pegmatites, Hidra anorthosite massif, southwestern Norway: Mechanics and fluid chemistry
- Interlayer potassium and its neighboring atoms in micas: Crystal-chemical modeling and XANES spectroscopy
- Effect of chemical environment on the hydrogen-related defect chemistry in wadsleyite
- Fracture toughness, hardness, and elastic modulus of kyanite investigated by a depth-sensing indentation technique
- Crystal chemistry of the natrojarosite-jarosite and natrojarosite-hydronium jarosite solid-solution series: A synthetic study with full Fe site occupancy
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- Titanium as a cathodoluminescence activator in alkali feldspars
- Biogenic vs. abiogenic magnetite nanoparticles: A XMCD study
- Solubility of andradite, Ca3Fe2Si3O12, in a 10 mol% NaCl solution at 800 °C and 10 kbar: Implications for the metasomatic origin of grandite garnet in calc-silicate granulites
- A 3D reconstruction of plagioclase crystals in a synthetic basalt
- Rudashevskyite, the Fe-dominant analogue of sphalerite, a new mineral: Description and crystal structure
- Birchite, a new mineral from Broken Hill, New South Wales, Australia: Description and structure refinement
- Crystal structure of synthetic Al4B2O9: A member of the mullite family closely related to boralsilite
- Interaction of gypsum with As(V)-bearing aqueous solutions: Surface precipitation of guerinite, sainfeldite, and Ca2NaH(AsO4)2·6H2O, a synthetic arsenate
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- Evidence for anomalously large degree of polymerization in Mg2SiO4 glass and melt
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