The location of Mn (MnO: 2.0 wt%) in fluorapatite from Lavra da Golconda, near Governador Valadares, Minas Gerais, Brazil

Abstract

The local structural features around Mn in a transparent pale blue Mn–bearing fluorapatite (MnO: 2.0 wt%) from Lavra da Golconda, Brazil were investigated by a combined analysis of single crystal X–ray diffraction and XAFS. The crystal structure with the optimized formula (Ca_4.83Mn²⁺_0.15Sr_0.02)P₃O₁₂F with space group P6₃/m, a = 9.384(2), c = 6.8842 (6) Å, Z = 2 has been refined to R = 1.92% for the unique 555 reflections (Mo K_α). The structural refinement suggests that Mn almost exclusively occupies the Ca1 site. The EXAFS analysis indicates that Mn at the Ca1 site is surrounded by nine oxygen atoms with six shorter bonds and three longer bonds. BVS calculated for the local environment around Mn shows good agreement with the expected valence state of Mn. The present EXAFS results suggest that the longer bond distances (Ca1–O3) in fluorapatite structures will not be affected by Mn due to weak bonding interactions.