JACHYMOVITE, (UO2)(8)(SO4)(OH)(14)CENTER-DOT-13 H2O, A NEW URANYL MINERAL FROM JACHYMOV, THE KRUSNE HORY MTS, CZECH-REPUBLIC, AND ITS COMPARISON WITH URANOPILITE

Jachymovite, (UO2)(8)(SO4)(OH)(14). 13H(2)O, is monoclinic, with space group P12, 1 or P12(1)/ml inferred from powder diffraction data, and with a = 18.553(8) Angstrom, b = 9.276(2)Angstrom, c = 13.532(7)Angstr om, beta = 125.56(2)degrees, V = 1894(2)Angstrom(3), Z = 2 and D-calc = 4.79 g . cm(-3). The strongest lines in XRD pattern are (d in Angstr om, I, hkl): 7.56 (100, 200), 7.13(48, 101), 3.771(34, 400), 3.554(20, 50-3), 3.206(13, 32-3), 3.234(10, 22-3), 2.052(8, 142). Jachymovite f orms minute acicular crystals up to 0.1 mm long that make up crystalli ne coatings up to some cm(2) on gangue. It has yellow colour, pale yel low streak, vitreous lustre, yellow fluorescence under UV light (254 a nd 366 nm) and its translucent. It also has very good cleavage paralle l to [010], conchoidal fracture, brittle tenacity. The mineral is biax ial negative with refraction indices alpha = 1.715(2), beta = 1.718(2) and gamma = 1.720(2) (589 nm), 2V(calc) = 78 degrees, pleochroism Y = pale yellow, Z = yellow. Chemical analysis yields an average composit ion of UO3 84.20, SO3 2.79, H2O 13.32, total 100.31 wt.%, leading to a formula (UO2)(8)(SO4)(OH)(14). 13H(2)O. The mineral formed as an alte ration product of strongly weathered uraninite, it occurs in the dolom ite-uraninite veins at Jachymov, Krusne hory Mts., Western Bohemia, Cz ech Republic, in association with gypsum, uranopilite and uraninite. T he name is for the locality Jachymov. Jachymovite is compared with ura nopilite and X-ray powder diffraction data, thermal analysis and infra red spectra for both minerals are given.