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Acta Crystallogr B Struct Sci Cryst Eng Mater. 2017 Oct 1;73(Pt 5):899-906. doi: 10.1107/S2052520617006588. Epub 2017 Sep 16.

Crystal structure of the OH-dominant gadolinite-(Y) analogue (Y,Ca)2(Fe,□)Be2Si2O8(OH,O)2 from Heftetjern pegmatite, Norway.

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Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432, Russian Federation.
Faculty of Geology, St Petersburg State University, University Embankment 7/9, St Petersburg 199034, Russian Federation.
Institute of Crystallography of Federal Scientific Research Centre `Crystallography and Photonics', Russian Academy of Sciences, Leninskii Prospekt 59, Moscow 119333, Russian Federation.
PO Box 32, N-1650 Sellebakk, Norway.
Faculty of Geology, Moscow State University, Vorobievy Gory, Moscow 119991, Russian Federation.
Fersman Mineralogical Museum of the Russian Academy of Sciences, Leninsky Prospekt 8-2, Moscow 117071, Russian Federation.
Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432, Russian Federation.
Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetny Per. 35, Moscow 119017, Russian Federation.


A hydroxyl-dominant analogue of gadolinite-(Y) (OH-Gad) has been discovered in the Heftetjern granitic pegmatite, southern Norway, in association with late-stage rare-earth-element containing minerals. The empirical formula, based on ten O atoms per formula unit, is (Y1.285Ca0.55Ce0.07La0.04Nd0.01)Σ1.955(Fe2+0.570.43)Be2.02Si1.995O8.48(OH)1.52. The mineral is monoclinic, space group P21/c, a = 4.7514 (10), b = 7.5719 (16), c = 9.9414 (2) Å, β = 90.015 (4)°, V = 357.663 (3) Å3 and Z = 2. The density calculated using the empirical formula is 3.903 g cm-3. The crystal structure was refined to R = 0.0217 for 776 reflections with I > 2σ(I). OH-Gad is isostructural with gadolinite-(Y) and it is characterized by the predominance of OH- over O2- at the anionic Ø-site. The refined crystal-chemical formula is: A(Y1.25Ca0.55Ce0.2)X(Fe2+0.570.43)ZBe2TSi2O8Ø[(OH)0.86O0.59(OH)*0.55] (Z = 2). The possible orientation and local environment of the hydroxyl group were suggested based on bond-valence sum calculations and geometrical analysis of the crystal structure. The infrared spectrum confirms disordering of H atoms. OH-Gad seems to be a potentially new mineral, the first simultaneously hydroxyl- and iron-dominant member of the gadolinite subgroup. It is an OH-analogue of gadolinite-(Y) and an Fe2+-analogue of hingganite-(Y).


Heftetjern; OH-dominant gadolinite-(Y); gadolinite-datolite group


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