Polymorphism is the ability of a substance to exist in different crystal types. A very typical example of polymorphism can be seen in chocolate, which contains cocoa butter. 

Cocoa butter is a polymorphic fat comprising three main triglycerides. They can crystallize in six different polymorphs with different melting points. These six phases of chocolate are generally numbered with Roman numerals in ascending order of melting temperature. The ideal one is the form V concerning appearance and taste. Nevertheless, form V is not the most stable form, so it requires a ‘tempering’ process to achieve the desired lipid crystal form. Unlike others, the form VI, which is hard, and hardly melts in the mouth, forms after several months only from form V.