British scientists around P. Mark Rodger, Department of Chemistry and Centre for Scientific Computing, University of Warwick, Coventry, UK, showed with metadynamics simulations that the chicken eggshell protein ovocleidin-17 induces the formation of calcite crystals from amorphous calcium carbonate nanoparticles.

Multiple spontaneous crystallization and amorphization events were simulated, suggesting that OC-17 acts as a catalyst by binding to amorphous calcium carbonate nanoparticles, transforming them to calcite nuclei, and then desorbing as the calcite begins to grow, thus leaving the OC-17 available to bind to another ACC nanoparticle. This catalytic cycle provides a mechanism for forming the polycrystalline mammillary caps that are deposited on the organic membrane as the first stage of eggshell formation.

… and some conclude, that therefore the egg can only exist if it has been created inside a chicken …

• Structural Control of Crystal Nuclei by an Eggshell Protein
  C. L. Freeman, J. H. Harding, D. Quigley, P. M. Rodger,
  Angew. Chem. Int. Ed. 2010, 49, 5135-5137.
  DOI: 10.1002/anie.201000679