Fluorcalciopyrochlore, A New Mineral Species From Bayan Obo, Inner Mongolia, P.R. China

Abstract

Abstract Fluorcalciopyrochlore, ideally (Ca,Na) 2 Nb 2 O 6 F, cubic, is a new mineral species (IMA2013-055) occurring in the Bayan Obo Fe-Nb-REE deposit, Inner Mongolia, People9s Republic of China. The mineral is found in a dolomite-type niobium rare-earth ore deposit. Associated minerals are dolomite, aegirine, riebeckite, diopside, fluorite, baryte, phlogopite, britholite-(Ce), bastnasite-(Ce), zircon, magnetite, pyrite, fersmite, columbite-(Fe), monazite-(Ce), rutile, and others. Crystals mostly form as octahedra {111}, dodecahedra {110}, and cubes {100}, or combinations thereof, and generally range in size from 0.01 to 0.3 mm. It is brownish-yellow to reddish-orange in color with a light yellow streak. Crystals of fluorcalciopyrochlore are translucent to transparent with an adamantine to greasy luster on fractured surfaces. It has a conchoidal fracture. No parting or cleavage was observed. The Mohs hardness is 5, and the calculated density is 4.34(1) g/cm 3 . The empirical formula is (Ca 1.14 Na 0.74 Ce 0.06 Sr 0.03 Th 0.01 Fe 0.01 Y 0.01 La 0.01 Nd 0.01 ) Σ2.02 (Nb 1.68 Ti 0.29 Zr 0.02 Sn 0.01 ) Σ2.00 O 6.00 (F 0.92 O 0.08 ) Σ1.00 on the basis of 7(O,F) anions pfu . The simplified formula is (Ca,Na) 2 Nb 2 O 6 F. The strongest four reflections in the X-ray powder-diffraction pattern [ d in A (I) hkl ] are: 6.040 (9) 1 1 1, 3.017 (100) 2 2 2, 2.613 (17) 0 0 4, 1.843 (29) 0 4 4, and 1.571 (15) 2 2 6. The unit-cell parameters are a 10.4164(9) A, V 1130.2(2) A 3 , Z = 8. The structure was solved and refined in space group Fd m with R = 0.05. The type material is deposited in the Geological Museum of China, Beijing, People9s Republic of China, catalogue number M12182.