The two unit cells used to describe the ZnS structure differ only in the location of the lattice points used to define them. Both are the same size and shape. In one cell, the lattice points are placed at the centers of sulfide ions. This cell has sulfide ions at the corners and centers of the faces.

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In the alternate cell, lattice points are placed at the centers of the zinc ions. This cell has zinc ions located at the corners and in the centers of the faces. The alternate cell is difficult to see here because it is partially buried in the structure.