Limousinite, BaCa[Be4P4O16]·6H2O, a new beryllophosphate mineral with a phillipsite-type framework

Autor: Pietro Vignola, Yannick Bruni, Andrea Risplendente, Fabrice Dal Bo, François-Xavier Châtenet, Nicolas Meisser, Julien Lebocey, Frédéric Hatert
Rok vydání: 2020
Předmět:
Zdroj: Canadian mineralogist 58 (2020): 815–827. doi:10.3749/canmin.2000007
info:cnr-pdr/source/autori:Hatert F., Dal Bo F., Bruni Y, Meisser N., Vignola P., Risplendente A., Chatenet F.X. & Lebochey J./titolo:Limusinite, BaCa[Be4P4O16]*6H2O, a new beryllophosphate mineral with a phillipsite-type framework/doi:10.3749%2Fcanmin.2000007/rivista:Canadian mineralogist/anno:2020/pagina_da:815/pagina_a:827/intervallo_pagine:815–827/volume:58
ISSN: 1499-1276
0008-4476
Popis: Limousinite, ideally BaCa[Be4P4O16]·6H2O, is a new beryllophosphate mineral discovered in the Vilatte-Haute pegmatite, Chanteloube near Razès, Limousin, Haute-Vienne, France. The new mineral is intimately associated with microcrystalline pale brown greifensteinite, black amorphous vitreous Mn-oxyhydroxide, triplite, and quartz. It forms isolated, partly corroded, colorless to snow-white crystals up to 0.9 mm long, showing rhombic cross sections. Limousinite is transparent with a vitreous luster, non-fluorescent, without cleavage planes; its calculated density is 2.58 g/cm3. Optically, the mineral is biaxial negative, α = 1.532(2), β = 1.553(3), γ = 1.558(2) (measured under 589 nm wavelength light), 2Vcalc. = 18°, non-dispersive, with Z parallel to the elongation of the prismatic crystals. Electron-microprobe analyses indicate an empirical formula of (Ba0.91K0.07)Σ0.98(Ca0.87Na0.05)Σ0.92[(Be3.87Al0.13)Σ4P4O16]·5.56H2O, calculated on the basis of 4 P atoms per formula unit, assuming 4 (Be + Al) pfu and a water content calculated from refined site-occupancy factors. A single-crystal structure refinement was performed to R1 = 4.90%, in the P21/c space group, with a = 9.4958(4), b = 13.6758(4), c = 13.4696(4) Å, β = 90.398(3)°, V = 1749.15(10) Å3, Z = 4. The crystal structure is characterized by a beryllophosphate framework similar to that of phillipsite-group zeolites, based on corner-sharing BeO4 and PO4 tetrahedra forming interconnected four- and eight-membered rings. Large cages within this zeolite framework contain Ba, Ca, and water molecules. Limousinite is the third known natural zeolite-type beryllophosphate, together with pahasapaite and wilancookite; it is also the first phosphate with a framework identical to that of a natural zeolite silicate.
Databáze: OpenAIRE
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