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Exploring the unusual occurrence, chemistry, and structural topology of åsgruvanite-(Ce), Ce16Ca5Al(SiO4)6(AsO3)8(CO3)2Cl3(ClF3)(OH)2, a new rare earth element (REE) mineral from Västmanland, Sweden

Authors

Taddei,  Alice
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Holtstam,  Dan
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Jonsson,  Erik
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/persons/resource/forhj

Förster,  H.-J.
4.3 Geoenergy, 4.0 Geosystems, Departments, GFZ Publication Database, GFZ Helmholtz Centre for Geosciences;

Andersson,  Stefan S.
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Appelt,  Oona
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, GFZ Helmholtz Centre for Geosciences;

Bindi,  Luca
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Citation

Taddei, A., Holtstam, D., Jonsson, E., Förster, H.-J., Andersson, S. S., Appelt, O., Bindi, L. (2025): Exploring the unusual occurrence, chemistry, and structural topology of åsgruvanite-(Ce), Ce16Ca5Al(SiO4)6(AsO3)8(CO3)2Cl3(ClF3)(OH)2, a new rare earth element (REE) mineral from Västmanland, Sweden. - European Journal of Mineralogy, 37, 6, 937-951.
https://doi.org/10.5194/ejm-37-937-2025


Cite as: https://gfzpublic.gfz.de/pubman/item/item_5037495
Abstract
Åsgruvanite-(Ce), ideally Ce16Ca5Al(SiO4)6(AsO3)8(CO3)2Cl3(ClF3)(OH)2, is a new mineral species (IMA–CNMNC 2025-004) from the Åsgruvan Fe-skarn deposit, Norberg, Västmanland, Sweden, which is directly related to the Bastnäs type of rare earth element (REE) mineralisations in the Palaeoproterozoic Bergslagen ore province. Åsgruvanite-(Ce) occurs as anhedral, occasionally elongated grains up to 400 µm. It is greyish green to nearly colourless, with a white streak and a vitreous to greasy lustre. Cleavage is distinct on {001} and less so on {100}; the mineral is brittle, and its fracture is uneven. The calculated density is 4.79(1) g cm−3. Åsgruvanite-(Ce) is optically uniaxial (+), with a refractive index above 1.8; the calculated average is 1.88 (Gladstone–Dale approach). Åsgruvanite-(Ce) crystallises in the trigonal system in space group P-3m1 (Z=1), with the following unit cell parameters: a=10.5728(6) Å and c=15.0899(11) Å. Åsgruvanite-(Ce) occurs in a magnetite–REE skarn, but its formation postdates the groundmass carbonate and skarn assemblage, and it is associated with late-stage calcite, dolomite, a dollaseite-like allanite group mineral, gadolinite-(), and a fluorocarbonate related to bastnäsite-(Ce), with variable F contents. The structure was refined to R1=6.23 % for 987 reflections. It is unique and consists of two alternating layers, A and B, along the c axis. Layer A (∼8.4 Å) has the composition [(Ce12Ca3)AlSi6(C1.50S0.50)Σ2.00O30(OH)2]15+. Layer B (∼6.7 Å) corresponds to the composition [(Ce4Ca2)AsO24Cl4F3]15−. These layers form tunnel-like features parallel to [100], which are partially occupied by Cl atoms. Spectroscopic data (infrared and micro-Raman) support the structural model.