Wurtzite (ZnS)/Zincite (ZnO)
Stoichiometry = AX
Space Group = P6₃mc (186)
a = ~ [2.698 - 4.592 angstroms]
c = ~ [4.379 - 7.51 angstroms]

Atomic Positions
       A      2b     1/3, 2/3, z       z ~ 0.0
       X      2b     1/3, 2/3, z       z ~ 0.38

Coordination Numbers/Geometry
       A      CN=4     Tetrahedral coordination
       X      CN=4      Tetrahedral coordination

Representative Compounds*
        Halides (5) - (i.e. AgI, CuBr)
        Carbides (1) - (i.e. a-SiC)
        Hydrides (1) - (CuH)
        Nitrides (5) - (i.e. AlN, InN)
        Oxides (2) - (BeO, ZnO)
        Sulfides, Selenides and Tellurides (12) - (i.e. CdS, ZnSe, MnTe)

*The numbers in parentheses are the number of compounds of each type found
in "Structure and Properties of Inorganic Solids" by Francis Galasso, Pergammon Press
(1970).
 

 
Description
The wurtzite structure is very similar to sphalerite, the difference being that sphalerite has a structure which can be derived from a cubic close packing of ions, while wurtzite is dervied from a hexagonal close packing scheme.  The hcp ABAB... stacking of the wurtzite structure is illustrated in the upper right hand figure. As you might expect, the energetics of these two structures are very similar. Though it is known that a subtle increase in the ionicity of the AX bonding tends to stabilize wurtzite with respect to sphalerite.