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Oxynatromicrolite, (Na,Ca,U)2Ta2O6(O,F), a new member of the pyrochlore supergroup from Guanpo, Henan Province, China

Published online by Cambridge University Press:  02 January 2018

Fan Guang ,
Ge Xiangkun ,
Li Guowu ,
Yu Apeng  and
Shen Ganfu
Fan Guang*
Affiliation:
Beijing Research Institute of Uranium Geology, 100029 Beijing, China
Ge Xiangkun
Affiliation:
Beijing Research Institute of Uranium Geology, 100029 Beijing, China
Li Guowu
Affiliation:
Laboratory of Crystal Structure, China University of Geoscinces (Beijing), 100083 Beijing, China
Yu Apeng
Affiliation:
Beijing Research Institute of Uranium Geology, 100029 Beijing, China
Shen Ganfu
Affiliation:
Chengdu Institute of Geology and Mineral Resources, 610082 Chengdu, China
*
*E-mail: [email protected]
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Abstract

A new mineral species of the pyrochlore supergroup, oxynatromicrolite (IMA2013-063), (Na,Ca,U)2Ta2O6O, was found in the No. 309 rare-metal granitic pegmatite vein, Guanpo, Lushi county, Henan Province, China, which is characterized by tantalum at theB site and oxygen at the Y site and is Na dominant at the A site. The mineral occurs as strongly metamict, and mostly euhedral octahedral crystals up to 0.05–0.20 mm across. The measured density of an unheated sample is 6.580(4) g cm–3, and the calculatedone is 6.506 g cm–3. Optically, the mineral is isotropic, with an index of refraction 1.999(5) and a reflectance of 11.88% (470 nm). When heated to 1000°C for 4 hours in N2, the mineral recrystallizes in the cubic system, with space group Fd3mand with unit-cell parameters similar those of other pyrochlore supergroup species: a = 10.420(6) Å, V = 1131.4(2) Å3. Electron microprobe analyses revealed the following composition of the mineral (in wt.%): Na2O 5.41, CaO 4.56, UO214.60, La2O3 0.16, Ce2O3 0.11, Nd2O3 0.13, PbO 0.62, Ta2O5 61.52, Nb2O5 8.21, Sb2O5 0.23, TiO2 0.05, SiO2 0.56, SnO2 0.29, F1.04, H2O 1.50 (calculated to correspond to 0.47 H2O pfu), F≡O –0.44, sum = 98.53%, which corresponds to the empirical formula (Na0.99Ca0.46U0.31Pb0.02La0.01H2O0.21)∑2.00(Ta1.58Nb0.35Si0.05Sn0.01Sb0.01)∑2.00O6 (O0.43F0.31H2O0.26)∑1.00, represented by the simplified formula (Na,Ca,U)2(Ta,Nb)2O6(O,F).Oxynatromicrolite crystallized during the late-stage of formation for the No. 309 pegmatite dyke and is associated with quartz, albite, potassium feldspar, muscovite, kaolinite, tantalite-Mn, stibiotantalite, pollucite, spodumene, montebrasite, Hf-rich zircon, a red tourmaline, polylithionite,trilithionite, luanshiweiite-2M1 (IMA2011-102) and a hydrated derivative of oxynatromicrolite.

Keywords

oxynatromicrolitenew mineral speciesmicrolite grouppyrochlore supergroupGuanpoHenanChina
Type
Research Article
Information
Mineralogical Magazine , Volume 81 , Issue 4 , August 2017 , pp. 743 - 751
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2017

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