Secondary uranium phosphates and silicates from Perus, Sao Paulo State, Brazil

Secondary uranium phosphates and silicates occur as placoid crystals and crusts, colored green to yellow, filling fractures in the tourmaline-bearing granitic pegmatite of Perus, northwestern part of the city of Sao Paulo, southeastern of Brazil. The following phosphates were identified by X-ray diffractometry, optical properties, EDS and wet chemical analysis: autunite, meta-autunite, meta-torbernite, chernikovite, meta-uranocircite, and phurcalite. Chernikovite is a new mineral name, superseding 'hydrogen autunite', whilst meta-uranocircite is described for the first time at Perus. Phurcalite was previously referred as 'mineral X from Perus'; a new structural formula Ca2(U O2)3 O2(P O4)2.7 H2 O is attributed to this species. Previous literature on Perus also mentions the occurrence of torbernite, bassetite and phosphuranylite, not yet identified by the authors. The presence of the following silicates has been verified: uranophane-alpha, uranophane-beta, haiweeite and barian weeksite. The last mineral, a first quotation for this locality, is the variety with the largest Ba content as yet described. The occurrence of meta-haiweeite needs confirmation. Opal (tridymite and cristobalite), secondary quartz, saponite and rhodochrosite occur associated to the uranium minerals. (author). 2 figs., 3 tabs