TY - JOUR

T1 - Cesiokenopyrochlore, the First Natural Niobate with an Inverse Pyrochlore Structure

AU - Agakhanov, Atali A.

AU - Kasatkin, Anatoly V.

AU - Britvin, Sergey N.

AU - Siidra, Oleg I.

AU - Pautov, Leonid A.

AU - Pekov, Igor V.

AU - Karpenko, Vladimir Yu.

N1 - Publisher Copyright: © 2021 Mineralogical Association of Canada. All rights reserved.

PY - 2021/2/26

Y1 - 2021/2/26

N2 - Cesiokenopyrochlore is a new mineral belonging to the pyrochlore group. It was discovered in a specimen of granitic pegmatite collected at Tetezantsio, Betafo region, Madagascar. The mineral forms rough equant crystals up to 0.05 mm in size intergrown with béhierite and rynersonite. Cesiokenopyrochlore is light-brown, translucent, with resinous luster. D calc. ¼ 5.984 g/cm 3. In reflected light it is light gray, isotropic, with strong light-brown internal reflections. The crystal structure was refined to R 1 ¼ 0.0212. The mineral is cubic, Fd -3m, a ¼ 10.444(1) A , V ¼ 1139.5(2) A 3, and Z ¼ 8. The strongest lines of the powder X-ray diffraction pattern [d, A , (I, %) (hkl)] are: 6.03 (37) (111), 3.70 (9) (220), 3.15 (100) (311), 3.02 (36) (222), 2.012 (17) (511, 333), 1.848 (19) (440), 1.576 (11) (622). The chemical composition is (wt.%; electron microprobe): Cs 2O 22.66, Na 2O 1.74, CaO 0.64, Nb 2O 5 20.87, Ta 2O 5 21.27, WO 3 30.67, H 2O (calc) 0.12, total 97.97. The empirical formula of the holotype specimen calculated on the basis of (NbþTaþW) ¼ 2 apfu and (OþOH) ¼ 6 apfu and written according to the pyrochlore-supergroup nomenclature is Na 0.29Ca 0.06(Nb 0.81W 0.69Ta 0.50) R2[O 5.93(OH) 0.07] R6Cs 0.83. The simplified formula of the holotype specimen is A 2(Nb,W,Ta) R2O 6Cs. Cesiokenopyrochlore is the first natural niobate to adopt the inverse pyrochlore structure.

AB - Cesiokenopyrochlore is a new mineral belonging to the pyrochlore group. It was discovered in a specimen of granitic pegmatite collected at Tetezantsio, Betafo region, Madagascar. The mineral forms rough equant crystals up to 0.05 mm in size intergrown with béhierite and rynersonite. Cesiokenopyrochlore is light-brown, translucent, with resinous luster. D calc. ¼ 5.984 g/cm 3. In reflected light it is light gray, isotropic, with strong light-brown internal reflections. The crystal structure was refined to R 1 ¼ 0.0212. The mineral is cubic, Fd -3m, a ¼ 10.444(1) A , V ¼ 1139.5(2) A 3, and Z ¼ 8. The strongest lines of the powder X-ray diffraction pattern [d, A , (I, %) (hkl)] are: 6.03 (37) (111), 3.70 (9) (220), 3.15 (100) (311), 3.02 (36) (222), 2.012 (17) (511, 333), 1.848 (19) (440), 1.576 (11) (622). The chemical composition is (wt.%; electron microprobe): Cs 2O 22.66, Na 2O 1.74, CaO 0.64, Nb 2O 5 20.87, Ta 2O 5 21.27, WO 3 30.67, H 2O (calc) 0.12, total 97.97. The empirical formula of the holotype specimen calculated on the basis of (NbþTaþW) ¼ 2 apfu and (OþOH) ¼ 6 apfu and written according to the pyrochlore-supergroup nomenclature is Na 0.29Ca 0.06(Nb 0.81W 0.69Ta 0.50) R2[O 5.93(OH) 0.07] R6Cs 0.83. The simplified formula of the holotype specimen is A 2(Nb,W,Ta) R2O 6Cs. Cesiokenopyrochlore is the first natural niobate to adopt the inverse pyrochlore structure.

KW - Cesiokenopyrochlore

KW - Cesium

KW - Crystal structure

KW - Granitic pegmatite

KW - Inverse pyrochlore

KW - Madagascar

KW - New mineral

KW - Niobate

KW - Pyrochlore group

KW - Tetezantsio

UR - http://www.scopus.com/inward/record.url?scp=85110276188&partnerID=8YFLogxK

U2 - 10.3749/canmin.2000056

DO - 10.3749/canmin.2000056

M3 - Article

VL - 59

SP - 149

EP - 157

JO - Canadian Mineralogist

JF - Canadian Mineralogist

SN - 0008-4476

IS - 1

ER -