Fluorbritholite-(Nd), Ca2Nd3(SiO4)3F, a new and key mineral for neodymium 
sequestration in REE skarns

Holtstam, Dan; Casey, Patrick; Bindi, Luca; Förster, H.-J.; Karlsson, Andreas; Appelt, Oona

doi:10.1180/mgm.2023.45

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Fluorbritholite-(Nd), Ca2Nd3(SiO4)3F, a new and key mineral for neodymium sequestration in REE skarns

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Holtstam, Dan
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Casey, Patrick
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Bindi, Luca
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Förster, H.-J.
4.8 Geoenergy, 4.0 Geosystems, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Karlsson, Andreas
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Appelt, Oona
3.6 Chemistry and Physics of Earth Materials, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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Citation

Holtstam, D., Casey, P., Bindi, L., Förster, H.-J., Karlsson, A., Appelt, O. (2023): Fluorbritholite-(Nd), Ca2Nd3(SiO4)3F, a new and key mineral for neodymium sequestration in REE skarns. - Mineralogical Magazine, 87, 5.
https://doi.org/10.1180/mgm.2023.45

Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5022724

Abstract

Fluorbritholite-(Nd), ideally Ca2Nd3(SiO4)3F, has been approved by the International Mineralogical Association (IMA2023–001) and constitutes a new member of the britholite group of the apatite supergroup. It occurs in skarn from the Malmkärra iron mine, Norberg, Västmanland (one of the Bastnäs-type deposits in Sweden), associated with calcite, dolomite, magnetite, lizardite, talc, fluorite, baryte, scheelite, gadolinite-(Nd) and other REE minerals. Fluorbritholite-(Nd) forms anhedral and small grains, rarely up to 250 μm across. They are brownish pink and transparent with a vitreous to greasy lustre. The mineral is brittle, with an uneven or subconchoidal fracture and lacks a cleavage. In thin section, the mineral is nonpleochroic, uniaxial (–). Dcalc = 4.92(1) g⋅cm−3 and ncalc = 1.795. The empirical chemical formula from electron microprobe (WDS) point analyses is (Ca1.62Nd0.97Ce0.83Y0.52Sm0.30Gd0.23Pr0.17La0.16Dy0.11Er0.03Tb0.03Ho0.01Yb0.01)Σ4.99(Si2.92P0.08As0.01)Σ3.01O12.00[O0.48F0.26(OH)0.14Cl0.10Br0.02]Σ1.00. The crystal structure of fluorbritholite-(Nd) was refined from single-crystal X-ray diffraction data to R1= 0.043 for 704 unique reflections. It belongs to the hexagonal system, space group P63/m, with unit cell parameters a = 9.5994(3), c = 6.9892(4) Å and V = 557.76(5) Å3 for Z = 2. Fluorbritholite-(Nd) and other britholite-group minerals are a major sink for neodymium in REE-bearing skarns of Bastnäs type.