ZnS exists in two main crystalline forms. This dualism is an example of polymorphism. In each form, the coordination geometry at Zn and S is tetrahedral. The more stable cubic form is known also as zinc blende or sphalerite.  The hexagonal form is known as the mineral wurtzite, although it also can be produced synthetically.  The transition from the sphalerite form to the wurtzite form occurs at around 1020 °C.