• journal_title：The Canadian Mineralogist
• Contributor：Igor V. Pekov ; Nikita V. Chukanov ; Natalia V. Zubkova ; Dmitry A. Ksenofontov ; László Horváth ; Aleksandr E. Zadov ; Dmitry Yu. Pushcharovsky
• Publisher：Mineralogical Association of Canada
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.48.1.95
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：48
• issue：1
• firstpage：95
• section：Articles

Lecoqite-(Y), ideally Na₃Y(CO₃)₃·6H₂O, a new mineral species, was discovered at the Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada. It is associated with microcline, albite, natrolite, gonnardite, aegirine, siderite, elpidite, gaidonnayite, zircon, franconite, dawsonite, rhodochrosite, cryolite, rutile, and sphalerite. Lecoqite-(Y) forms radiating, spray-like aggregates in compact, tightly packed masses to 2.5 cm across, composed of flexible, extremely thin, capillary crystals up to 2.5 cm long and up to 0.01 mm thick. Individuals are colorless, and aggregates are white. The luster is strikingly silky. D(calc.) = 2.358 g/cm³. Lecoqite-(Y) is optically uniaxial positive, ω = 1.521(3), ε = 1.497(3). The IR spectrum is unique. The chemical composition (electron microprobe, H₂O by modified Penfield method, CO₂ by selective absorption, average results) is: Na₂O 19.22, CaO 0.03, Y₂O₃ 17.95, Nd₂O₃ 0.54, Sm₂O₃ 0.41, Gd₂O₃ 0.75, Dy₂O₃ 3.31, Ho₂O₃ 1.12, Er₂O₃ 3.20, Yb₂O₃ 1.48, CO₂ 27.0, H₂O 23.4, total 98.41 wt.%. The empirical formula calculated for 15 O apfu is: Na_2.94(Y_0.755Dy_0.085Er_0.08Yb_0.035Ho_0.03Gd_0.02Nd_0.015 Sm_0.01)_∑1.03(CO₃)_2.91(OH)_0.21(H₂O)_6.06. Lecoqite-(Y) is hexagonal, P6₃, a 11.316(4), c 5.931(2) Å, V 657.7(4) ų, Z = 2. The crystal structure was established from X-ray powder data by the Rietveld method, based on the model of the isostructural synthetic Ln-free carbonate Na₃Y(CO₃)₃·6H₂O. Final agreement factors are: R_p = 0.0468, R_wp = 0.0657, R_Bragg = 0.0343, R_F = 0.0356. No mineral is closely related to lecoqite-(Y) in terms of structure. In the structure of lecoqite-(Y), REE atoms (REE = Y + Ln) are surrounded by six O atoms of CO₃ groups and three H₂O molecules to form a tricapped triangular prism. The Na atoms are centered in distorted octahedra [NaO₄(H₂O)₂], which link to form infinite corrugated chains along c. The strongest five lines of the X-ray powder pattern [d in Å (I)(hkl)] are: 9.82(57)(100), 5.081(100)(101), 3.779(39)(201), 2.627(39)(112), 2.471(37)(131). Lecoqite-(Y) is named in memory of P.É. Lecoq de Boisbaudran (1838–1912), outstanding French chemist and specialist in the spectroscopic analysis of minerals and synthetic compounds, who made a great contribution to the chemistry of the rare-earth elements. The Levinson suffix modifier -(Y) is in line with the dominance of yttrium over other rare-earth elements in the mineral. The cotype specimens are deposited in the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow, and the Canadian Museum of Nature, Ottawa.