In calcium fluoride, having the fluorite structure the coordination numbers for the calcium ion Ca2+ and fluoride ion (F−) are
8 and 4
CaF2→AB2 type structure (Fluorite type)
Ca2+→ Face central cubic lattice points
F−→ tetrahedral voids
Each Ca2+ surrounded by 8F− ions
Each F− surrounded by 4Ca2+ ions
C.N. of Ca2+ and F− are 8 and 4 respectively