What is packing polymorphism

When polymorphism exists as a result of change in crystal packing, it is called packing polymorphism. Polymorphism can also result from the existence of dissimilar conformers of the similar molecule in conformational polymorphism. In pseudopolymorphism the dissimilar crystal types are the result of  hydration or  solvation. An example of an organic polymorph is  glycine, which is able to form  monoclinic and  hexagonal crystals.  Silica is known to form many polymorphs, the most significant of which are; α-quartz, β-quartz,  tridymite, cristobalite, coesite, and stishovite.