Bulletin Mineralogie Petrologie

Plášil Jakub, Sejkora Jiří, Čejka Jiří, Pavlíček Radim, Babka Karel, Škoda Radek

Ročník 24, číslo 2 (2016), strana 298-303

boltwoodite, chemical composition, Raman spectroscopy, uranium deposit, Kladská, Czech Republic, powder X-ray diffraction data

Rare uranyl mineral boltwoodite, was found in the mine dump material of the abandoned uranium deposit Kladská, Slavkovský les Mountains, western Bohemia, Czech Republic. It occurs there as yellow to yellowish orange crystalline aggregates, veinlets and coatings in hydrothermally altered porphyric granite in association with uranophane. Its aggregates are usually composed from very thin acicular crystals. Well-formed boltwoodite crystals up to 2 mm in length in tiny cavities of crystalline aggregates of boltwoodite were observed only rarely. It is monoclinic, space group P2₁/m, the unit-cell parameters refined from X-ray powder diffraction data are: a 7.072(7), b 7.060(4), c 6.654(6) Å, β 105.06(7)° and V 320.8(5) ų. Chemical analyses of boltwoodite correspond to the empirical formula (K_0.62Pb_0.04)_Σ0.66(UO₂)_0.96(SiO₃OH)_1.00 . 1.5H₂O on the basis of Si = 1 apfu. The Raman spectrum of boltwoodite and its tentative interpretation are given. The origin of boltwoodite at Kladská is interpreted as product of late hydrothermal fluids which altered uraninite and granitic rocks.

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