Enantiotropy - one of two types of polymorphism - is characterized by reversibility (transition) of polymorphic modifications from one to another at certain temperatures and pressures. An example of enantiotropy is the transition of quartz to a high-temperature variety of SiO 2 - tridymite .
The second type - monotropy - one polymorphic modification (unstable) can transfer to another (stable), but the reverse transition is impossible. An example of monotropy is the transition of marcasite to pyrite . Carbon modifications — graphite and diamond — are monotropic, where the shape of graphite is stable.