The Influence of Organically Bound Minerals on the Process of Shell Construction

If ‘the aim of biomineralisation is stability’, then with reference to the hen’s egg such stability is essential if the calcified package, constructed over a period of 20 hours, is to meet the demands of the developing embryo or withstand the rigours of selection, packaging and travel en route to the table. The pattern of mineralisation in which calcite, the most stable polymorph of calcium carbonate precipitates in an a-cellular milieu regulated by a variety of protein profiles, follows a specific design. The morphology of each of the six layers which comprise the ‘true’ shell is quite distinct but in terms of shell strength they are interdependent. Of these perhaps the mammillary (basal) layer plays the most crucial role insofar as its morphology is easily altered by a range of internal and external variables including disease and bird age.