Polymorphism
is the term used to denote crystal systems where a substance can exist in
diVerent crystal packing arrangements, but all of which are characterized by exactly
the same elemental composition. Other crystal variations are known where a given
substance exists in diVerent crystal packing arrangements, but each of which exhibits
a diVerent elemental composition. Since this latter phenomenon usually
involves the inclusion of one or more solvent molecules in the crystal, the term
solvatomorphism has been coined to replace the inconsistent nomenclature used over
the years.