engleski

REE-bearing petscheckite from Tiltvika, Nordland, Norway, and its heating products

X-ray powder-diffraction investigation of a mineral sample from the Tiltvika granite pegmatite, Norway, shows the presence of a metamict phase with ferrocolumbite inclusions. On heating at 650°C for 21 hours, the diffraction pattern of petscheckite, a hexagonal mineral with idealized formula U4+Fe2+(Nb, Ta)2O8, is observed. The Tiltvika petscheckite is rich in REEs and has the general formula (U, REE)(Fe2+, Fe3+)(Nb, Ta)2(O, OH)8. Its unit-cell parameters are a = 6.42(2), c = 4.02(1) &Aring ; ; ; . Heating at 1000°C for 21 hours yields a phase with columbite-type structure and a pattern very close to that reported for heated “ wolframoixiolite” . Assuming space group Pcan, this phase has unit-cell parameters a = 5.005(5), b = 14.05(2), c = 5.64(1) &Aring ; ; ; . The high content of a-emitting uranium could explain the metamictization of a primary petscheckite. On the other hand, it is possible that an unknown primary mineral with complex composition has disintegrated into micro-exolutions of phases with simple stoichiometry, which have recombined to petscheckite on heating at 650&ordm ; ; ; C. For practical purposes, however, petscheckite as a metamict mineral species must be defined by its chemical composition and the characteristic X-ray powder pattern that it gives on heating to 650&ordm ; ; ; C.

petscheckite; ferrocolumbite; metamict state; granite pegmatite; Tiltvika; Norway

nije evidentirano