– Ca2+ 8 (cubic) : F– 4 (tetrahedral)
Ca2+ with F– in all Td holes
Polyhedra – Edge-sharing , edge-sharing
Cations form the cubic close packing while anions fill all tetrahedral holes.
Ca2+ ions are coordinated in cubic fashion (CN=8) while F– ions are tetrahedrally coordinated (CN=4)
(a) The fluorite structure and (b) its projection representation. This structure has a ccp array of cations and all the tetrahedral holes are occupied by anions.
Related Structure: Antifluorite (Na2O)