In calcium fluoride, having the fluorite structure, the coordination numbers for calcium ion Ca2+and fluoride ion  F- are

In fluorite structure, Ca2+ ions are in the face centred cubic arrangement. Each Ca2+ is connected to 4F- ions below it and to another set of 4F- ions above iti.e. Ca2+ has a coordination number of 8 and each F- ion has a coordination number 4 .