A type of ionic crystal structure in which the anions have a hexagonal close packed arrangement with the cations occupying one type of tetrahedral hole. Each type of ion has a coordination number of 4. Examples of this structure are found in ZnS, ZnO, AlN, SiC, and NH4F.
http://www.chemtube3d.com/solidstate/_wurtzite(final).htm An interactive version of the structure