Acta Musei Moraviae

Revision of the occurrence of vanadium-rich fissure phosphates at Medkovy Kopce near Hlinsko, Czech Republic

During the research of secondary fissure phosphates of the Bohemian Massif, the historically mentioned localities in the vicinity of Hlinsko were newly investigated. This paper further characterizes the occurrences of fluorwavellite, variscite, cacoxenite and crandallite in fissures of Silurian graphite-rich metasedimentary rocks at the Medkovy Kopce northwest of Hlinsko (Pardubice Region, Czech Republic). Fluorwavellite forms orange-yellow, light yellow and blue-grey radially rayed aggregates 2–4 mm in size. Its empirical formula is (Al_2.97V³⁺_0.02K_0.01)Σ_3.00[(PO₄)_1.97(VO₄)_0.03]Σ_2.00[F_0.72(OH)_2.27]Σ2_.99·5H₂O and refined unit-cell parameters are a 9.631(3), b 17.360(5), c 6.990(2) Å and V 1168.8(6) ų. Three varieties of variscite have been observed: yellow-green translucent spherical aggregates up to 1 mm in size with empirical formula (Al_1.00Fe_0.01)Σ_1.01[(PO₄)_0.99(VO₄)_0.01]_1.00·2H₂O; thin light green finely kidney-shaped crusts with empirical formula (Al_0.95Fe_0.03Mg_0.01)Σ_0.99(PO₄)1_.00·2H₂O and chalky white solid spherical or powdery aggregates with empirical formula (Al_1.05Fe_0.02Mg_0.01)Σ_1.08(PO₄)_1.00·2H₂O. Unit-cell parameters of all types of variscite are given in the text. Cacoxenite forms orange crusts up to 0.2 mm thick with empirical formula (Fe³⁺_19.76Al_3.81Mg_0.33Ca_0.07)Σ_23.97O_6.00[(PO₄)_16.76(VO₄)_0.24]Σ_17.00(OH)_8.53·75H₂O and its structure was verified by Raman spectroscopy.