Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Jiří Sejkora, Jakub Kristek, Pavel Škácha, Zdeněk Dolníček

Uramphite from the Nová Ves pod Pleší (Czech Republic), the third world occurrence - description and vibrational spectroscopy

Journal of Geosciences, volume 69 (2024), issue 3, 173 - 182

DOI: http://doi.org/10.3190/jgeosci.395

We have studied the rare ammonium uranyl phosphate mineral, uramphite, from the small uranium occurrence Nová Ves pod Pleší, central Bohemia (Czech Republic). It has been found on a few specimens and forms rare groups up to 1 mm in size in small vugs of limonite veins in altered rocks in association with meta-autunite, metatorbenite and churchite-(Y). Uramphite is pale yellow to light greenish yellow with a pale yellow streak and shows weak fluorescence in a pale yellow hue under 254 nm and 366 nm UV-radiation, respectively. Uramphite crystals are transparent to translucent and have an intensive vitreous luster. The mineral is very brittle and at least one system of perfect cleavage along {001} was observed. The quantitative electron-microprobe chemical analyses of uramphite agree well with the proposed ideal composition and correspond to the following empirical formula [(NH₄)_0.79Na_0.12K_0.07Ca_0.03]_Σ1.01(UO₂)_1.00(PO₄)_1.00·3H₂O (on the basis of 1 P atom pfu). Uramphite is tetragonal, space group P4/ncc, with the unit-cell parameters refined from X-ray powder diffraction data: a = 7.0292(11), c = 18.092(2) Å, V = 893.9(2) ų. Vibrational (Raman and infrared) spectroscopy documented the presence of molecular water, ammonium, uranyl, and phosphate groups in the crystal structure of uramphite.