Hydroxyplumbopyrochlore, (Pb1.5, □0.5)Nb2O6(OH), a new member of the pyrochlore group from Jabal Sayid, Saudi Arabia. (10th October 2020)

• Record Type: Journal Article
• Authors: Li, Ting; Li, Ziying; Fan, Guang; Fan, Honghai; Zhong, Jun; Jahdali, Naser S.; Qin, Mingkuan; Jehani, Abdullah M.; Wang, Fenggang; Nahdi, Mubarak M.
• Is Part Of: Mineralogical magazine. Volume 84:Number 5(2020)
• Page Start: 785
• Page End: 790
• Publication Date: 2020-10-10
• Subjects: hydroxyplumbopyrochlore, -- pyrochlore supergroup, -- new mineral, -- crystal structure, -- Saudi Arabia; Mineralogy -- Periodicals; Mineralogy -- Great Britain -- Periodicals; 549.05
• DOI: 10.1180/mgm.2020.69
• Languages: English
• ISSNs: 0026-461X

Abstract

ABSTRACT: A new mineral species of the pyrochlore supergroup, hydroxyplumbopyrochlore (IMA2018-145), (Pb1.5, □0.5 )Nb2 O6 (OH), has been discovered in the Jabal Sayid peralkaline granitic complex of the Arabian Shield, Saudi Arabia. It is associated with quartz, microcline, 'biotite', rutile, zircon, calcite, rhodochrosite, columbite-(Fe), goethite, thorite, bastnäsite-(Ce), xenotime-(Y), samarskite-(Y), euxenite-(Y), hydropyrochlore and fluornatropyrochlore. Hydroxyplumbopyrochlore usually shows euhedral octahedra, slightly rhombic dodecahedra and cubes or their combination (0.01–0.06 mm). The mineral is pale yellow to pale brown, transparent with white streak, and has adamantine to transparent lustre. It is brittle with conchoidal fracture. No cleavage or parting are observed. It is isotropic and non-fluorescent. The average microhardness is 463.4 kg mm –2 . The calculated density is 6.474 g cm –3 . Hydroxyplumbopyrochlore belongs to the cubic crystal system and exhibits the space group Fd $\bar{3}$ m with unit-cell parameters a = 10.5456(6) Å, V = 1172.8(2) Å 3 and Z = 8. Electron microprobe analysis gave (6-point average composition, wt.%): CaO 0.32, SrO 0.16, FeO 0.17, Ce2 O3 0.07, Pr2 O3 0.02, PbO 51.69, Nb2 O5 40.06, SiO2 0.05, TiO2 1.68, Ta2 O5 4.74, H2 Ocalc 0.95, total 99.90, yielding the empirical formula (Pb1.34 Ca0.03 Fe0.01 Sr0.01 □0.61 )Σ2 (Nb1.75 Ti0.12 Ta0.12 Si0.01 )Σ2 O6 (OH0.53 O0.08 □0.39 )Σ1, where □ = vacancy. The Raman spectrum of hydroxyplumbopyrochlore contains the characteristic bands of O–H vibrations and no bands for H2 O vibrations.