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Formula: Gd(PO4)
Phosphate of gadolinium,
xenotime group, tetragonal
paramorph of monoclinic
monazite-(Gd)
Crystal System: Tetragonal
Specific gravity: 5.55 calculated for the ideal formula and 5.26 for the empirical formula
Environments
Xenotime-(Gd) is a new mineral, approved in 2022 and to date (December 2024) reported only from the type locality.
Localities
At the type locality, the Zimná Voda uranium occurrence, Prakovce, Gelnica District, Košice Region, Slovakia,
xenotime-(Gd) forms rare crystal domains (≤20 μm, usually ≤10 μm in size) in
gadolinium-rich xenotime-(Y)
crystals (≤100 μm in size), in association with monazite group minerals,
uraninite, fluorapatite and
uranyl arsenates–phosphates. The
hydrothermal REE – uranium –
gold mineralisation occurs in a
quartz–muscovite vein, hosted in
Palaeozoic (538.8 to 251.9 million years ago) phyllites near exocontact
with Permian (298.9 to 251.9 million years ago) granites.
This exotic REE signature and precipitation of
gadolinium-bearing minerals is a product of selective complexing and
enrichment in middle REE in low-temperature hydrothermal fluids by
alteration of uraninite, brannerite
and fluorapatite on a micro-scale. The existence of xenotime-(Gd)
and monazite-(Gd) is the first naturally documented
dimorphism (paramorphism) among
REE phosphates. In addition, xenotime-(Gd) is only the third
approved gadolinium-dominant mineral, after
lepersonnite-(Gd) and
monazite-(Gd)
(MM 88.5.613-622).
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