ZnS, Zinc Sulphide, Zinc Blend, Wurtzite
Zinc sulphide exists with two different crystal structures, the cubic zinc blend (top diagram) and the hexagonal Wurtzite (lower diagram). 

In the zinc blend structure the sulphur ions form an fcc structure and the zinc ions occupy half of the tetrahedral sites in this structure to attain charge neutrality. The crystal has a lattice parameter of 0.541 nm. The crystal structure is also known as diamond cubic and may be thought of as two interpenetrating fcc lattices, one for sulphur the other for zinc, with their origins displaced by one quarter of a body diagonal.

The hexagonal wurtzite structure has the sulphur ions in an hcp array and one-half of the tetrahedral sites in this structure are occupied by zinc ions. The crystal has a basal lattice parameter, a = 0.233 nm and c/a = 1.63.

From: Kingery, Bowen and Uhlmann, "Introduction to Ceramics," Wiley (1976)