Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Jakub Plášil, Jiří Čejka, Jiří Sejkora, Jan Hloušek, Viktor Goliáš

New data for metakirchheimerite from Jáchymov (St. Joachimsthal), Czech Republic

Journal of Geosciences, volume 54 (2009), issue 4, 373 - 384

DOI: http://dx.doi.org/10.3190/jgeosci.057



Metakirchheimerite was found only on a few samples from the Jan Evangelista vein at the “Adit level” of the Svornost shaft, Jáchymov (St. Joachimsthal) ore district, Krušné Hory/Erzgebirge Mountains, Czech Republic. It forms rare crystalline aggregates consisting of fine tabular crystals which reach 0.1 mm in size, which are very brittle, having light pink to light orange colour, with a high vitreous lustre. Metakirchheimerite crystalline aggregates occur on carbonate gangue with disseminated primary minerals: arsenopyrite, uraninite and skutterudite. Studied metakirchheimerite is a (sub-)recent alteration product of the primary minerals, connected to the old open mine adit environment. According to electron microprobe analyses, the empirical formula of metakirchheimerite can be expressed, based on As + P = 2 apfu, as:
(Co0.53Mg0.25Ni0.08Zn0.07Fe0.05Ca0.03)Σ1.01(UO2)2.07[(AsO4)1.99(PO4)0.01)]Σ2.00.8H2O.
Metakirchheimerite from Jáchymov exhibits an extensive cationic substitution trend of the metanováčekite component. The diffraction pattern of metakirchheimerite is consistent with a triclinic symmetry inferred from the single-crystal study of the synthetic metakirchheimerite analogue. Refined unit-cell parameters for the triclinic space group P-1 are a 7.210(4) Å, b 9.771(6) Å, c 13.252(9) Å, α 75.39(4)°, β 83.94(6)°, γ 81.88(6)° with unit-cell volume V 892(1) Å3. Both infrared and Raman spectra of metakirchheimerite exhibited stretching and bending vibrations of (UO2)2+, (AsO4)3-, (PO4)3- and H2O groups. The vibration bands of all these units were tentatively assigned. The U-O bond lengths in uranyl and O-H…O hydrogen bond lengths, which were inferred from the spectra, are consistent with published crystal structure data for a synthetic analogue of metakirchheimerite.

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ISSN: 1802-6222

E-ISSN: 1803-1943