Arsenuranospathite, Al(UO_2)_2(AsO_4)_2F centre dot 20H_2O: Formula revision and relationships with allied uranyl arsenates and phosphates

摘要

A representative collection of specimens with arsenuranospathite and related minerals (including low-hydrated and F-deficient analogues of arsenuranospathite, as well as their PO_4-dominant counterparts) from the type locality of arsenuranospathite (Menzenschwand, Schwarzwald, Germany) has been investigated using electron-microprobe analysis, TG, X-ray powder diffraction and IR spectroscopy. The results obtained, together with related data from literature sources, undoubtedly demonstrate that the name arsenuranospathite is applied, at least, to two different species: proper arsenuranospathite (As-dominant mineral, closely related to of uranospathite, idealized formula Al(UO_2)_2(AsO_4)_2F centre dot 20H_2O, orthorhombic, a = 30.070 A, b = 7.147 A, c = 7.193 A; V = 1545.8 A~3, Z= 2), and its partially dehydrated counterpart, Al(UO_2),(AsO_4)_2F centre dot nH_20 (n = 8-10), tetragonal or pseudo-tetragonal, a = 7.246 A,c = 20.79A; V= 1091.6 A~3,Z = 2.