Abstract
Supergene Bi mineralization with namibite, bismutoferrite and bismutite was found on a quartz-fluorite vein Nadějná near the Kotlina in the Krušné hory Mts. (Czech Republic). Namibite forms green coatings on the cracks of fluorite veins and more rarely dark green glassy lustrous, hedgehog-shaped aggregates up to 0.2 mm in size formed by flat needle-like crystals. The unit-cell parameters of namibite refined from the powder X-ray data are: a 6.2096(18), b 7.395(2), c 7.4708(18) Å, α 90.1(2)°, β 108.73(15)°, γ 107.45(19)° and V 308.09(15) Å3. Its chemical analyses correspond to the empirical formula (Cu0.93Fe0.03Ca0.01)Σ0.97(BiO)1.79(V0.97P0.02Cr0.01)Σ1.00O4(OH)0.75. Bismutoferrite forms yellow powdery aggregates in cracks and in small cavities of fluorite. Its chemical analyses correspond to the empirical formula (Fe1.91 Cu0.03Mg0.02Al0.02Ca0.01)Σ1.99Bi0.92(SiO4)2.00(OH)0.68. Bismutite in the fluorite vein forms yellow-white pseudomorphoses probably after the acicular crystals of primary Bi sulfide (emplectite or bismuthinite) up to 2 mm long. Study of Raman spectra was performed for all studied minerals.
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