Publication details

Plavnoite, a new K-Mn member of the zippeite group from Jachymov, Czech Republic

Authors

PLÁŠIL Jakub ŠKACHA Pavel SEJKORA Jiří KAMPF Antony ŠKODA Radek ČEJKA Jiří HLOUŠEK Jan KASATKIN Anatoly PAVLÍČEK Radim BABKA Karel

Year of publication 2017
Type Article in Periodical
Magazine / Source European Journal of Mineralogy
MU Faculty or unit

Faculty of Science

Citation
Doi http://dx.doi.org/10.1127/ejm/2017/0029-2583
Keywords plavnoite; uranyl sulfate hydrate; new mineral; zippeite group; crystal structure; chemical composition
Description The new mineral plavnoite (IMA2015-059), ideally K0.8Mn0.6[(UO2)(2)O-2(SO4)]center dot 3.5H(2)O, is a member of the zippeite group. It was found in the Plavno mine, in the eastern part of the Jachymov ore district, Western Bohemia, Czech Republic, where it occurs as a supergene alteration phase formed by hydration-oxidation weathering of uraninite in hydrothermal U-veins. It was found to be associated with marecottite, magnesiozippeite, blatonite and gypsum. The mineral occurs as reddish to reddish-orange thin blades, elongated on [0 0 1] and flattened on {0 1 0}, which are intergrown in globular aggregates up to 0.5 mm across. Crystals are transparent with a vitreous to silky lustre. The streak is pale orange. The mineral is non-fluorescent under both long- and short-wave ultraviolet (UV) radiation. The Mohs hardness is about 2. Crystals are brittle with perfect {0 1 0} cleavage and uneven fracture. The density calculated from the empirical formula is 4.926 g cm(-3). Optically, plavnoite is biaxial (+), with alpha = 1.740(5), beta = 1.770(5), gamma = 1.850(5) (measured in white light). The measured 2V is 64.6(4)degrees; the calculated 2V is 65.3 degrees. Dispersion could not be observed; no pleochroism was observed. Electron-microprobe analyses yielded the empirical formula (based on 2 U atoms per formula unit,apfu) K-0.77(Mn0.51Zn0.04Ni0.03Mg0.02)(Sigma 0.60)[(UO2)(2)O-1.08(OH)(0.92)(SO4)(0.96)(SiO4)(0.24)](H2O)(3.50). Plavnoite is monoclinic, C2/c, a = 8.6254 (16), b = 14.258(3), c = 17.703(4) angstrom, beta = 104.052(18)degrees, V = 2122.0(8) angstrom(3) and Z = 8. The structure (R-1 = 4.99% for 989 reflections with 1 > 3 sigma[I]) contains UO7 pentagonal bipyramids and SO4 tetrahedra forming sheets of the well-known zippeite topology. The interlayer region contains infinite zig-zag chains of corner-sharing Mn2+phi(6) octahedra (phi=O, H2O) with K-centred polyhedra. The K atom sits at the partially occupied, mixed K/O site, the non-shared corner of the Mn2 octahedron. The mineral is named after the type locality - the Plavno mine.
Related projects:

You are running an old browser version. We recommend updating your browser to its latest version.

More info