Ionic Crystal Structures: Comprehensive Table

Structure	Anion Lattice	Cation Position	CN (cat:an)	$r^{+}$ / $r^{-}$	Z (f.u.)	Examples
NaCl (Rock Salt)	FCC ( $Cl^{-}$ )	ALL octahedral voids	6:6	0.414–0.732	4	NaCl, KCl, MgO, CaO, FeO
CsCl	Simple cubic ( $Cl^{-}$ )	Body centre	8:8	> 0.732	1	CsCl, CsBr, CsI
ZnS (Zinc Blende)	FCC ( $S^{2-}$ )	HALF tetrahedral voids	4:4	0.225–0.414	4	ZnS, CuCl, SiC
Fluorite ( $CaF_{2}$ )	— ( $Ca^{2+}$ in FCC)	$F^{-}$ in ALL tet voids	8:4	0.732–1.0	4	$CaF_{2}$ , $BaF_{2}$ , $SrF_{2}$
Antifluorite ( $Na_{2}O$ )	FCC ( $O^{2-}$ )	$Na^{+}$ in ALL tet voids	4:8	—	4	$Na_{2}O$ , $Li_{2}O$ , $K_{2}O$
Spinel ( $AB_{2}O_{4}$ )	FCC ( $O^{2-}$ )	A in 1/8 tet; B in 1/2 oct	4,6:4	—	8	$MgAl_{2}O_{4}$ , $Fe_{3}O_{4}$

Note on $CaF_{2}$ : In fluorite, the cation ( $Ca^{2+}$ ) forms FCC — NOT the anion. This is opposite to NaCl, ZnS, antifluorite where the anion forms FCC. $Ca^{2+}$ in FCC gives 8 tetrahedral voids; all 8 filled by $F^{-}$ → $CaF_{2}$ (4 formula units per cell).