Structural and compositional data for childrenite from the Homolka granite, Czech Republic

Members of the childrenite–eosphorite series, ideally (Feinline-formula_1−xMninline-formula_x)AlPOinline-formula₄(OH)inline-formula₂⋅Hinline-formula₂O, from the highly evolved Homolka granite, in the southern Czech Republic, were characterized using a multi-analytical approach. They occur as anhedral grains, up to inline-formula∼0.2 mm in size, associated with quartz, muscovite, albite, and K-feldspar. Tiny inclusions of probable uraninite have been observed. Backscattered electron images reveal a patchy zoning of these members of the childrenite–eosphorite series, related to an uneven distribution of Fe and Mn. On the basis of electron microprobe analysis, the average composition of the studied material is (Feinline-formula_0.68Mninline-formula_0.28Cainline-formula_0.03)_Σ0.99Alinline-formula_0.96(Pinline-formula_1.04Siinline-formula_0.01)_Σ1.05Oinline-formula_4.00(OH)inline-formula_2.09⋅0.91Hinline-formula₂O, thus corresponding to childrenite. Unit-cell parameters of this species are inline-formulaa=6.9226(9), inline-formulab=10.4081(13), inline-formulac=13.3957(17) Å. Its crystal structure was refined in the space group Cmca down to inline-formulaR₁=0.0295 on the basis of 602 unique reflections with inline-formulaF_o>4σ(F_o) and 66 refined parameters. The crystal structure analysis agrees with the results of electron microprobe analysis and suggests that, in the studied material, Fe occurs in the divalent oxidation state only. Crystal structure data are also consistent with the Raman spectrum collected on the same grain that was structurally characterized, confirming the occurrence of POinline-formula₄ groups only in childrenite.