Protein crystallization
The idea of creating a protein crystal is usually associated with X-ray crystallography which is used for studying the molecular structure of proteins. (It rarely occurs in nature however some have been observed.)[1]
In order to cause protein crystallization, the concentration of the protein in the solution has to be greater than the solubility limit.[2]
Upon meeting these conditions (supersaturation) the protein molecules can arrange together in repeating units and are stuck by non-covalent interactions.