FLUORCALCIOPYROCHLORE, A NEW MINERAL SPECIES FROM BAYAN OBO, INNER MONGOLIA, PR CHINA

摘要

Fluorcalciopyrochlore, ideally (Ca, Na)(2)Nb2O6F, cubic, is a new mineral species (IMA2013-055) occurring in the Bayan Obo Fe-Nb-REE deposit, Inner Mongolia, People's 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 (Ca1.14Na0.74Ce0.06Sr0.03Th0.01Fe0.01Y0.01La0.01Nd0.01)(Sigma 2.02)(Nb1.68Ti0.29Zr0.02Sn0.01)(Sigma 2.00)O-6.00(F0.92O0.08)(Sigma 1.00) on the basis of 7(O, F) anions pfu. The simplified formula is (Ca, Na) 2Nb2O6F. The strongest four reflections in the X-ray powder-diffraction pattern [d in angstrom (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 alpha 10.4164(9) angstrom A, V 1130.2(2)angstrom(3), Z = 8. The structure was solved and refined in space group Fd (3) over barm with R = 0.05. The type material is deposited in the Geological Museum of China, Beijing, People's Republic of China, catalogue number M12182.