what are the two main functions of the eggshell
Eggshell The bird egg is a fertilized gamete (or, in the case of some birds, such as chickens, possibly unfertilized) located on the yolk surface and surrounded by albumen, or egg white. The albumen in turn is surrounded by two shell membranes (inner and outer membranes) and then the eggshell. The chicken eggshell is 95[citation needed]-97%[1] calcium carbonate crystals, which are stabilized by a protein matrix.[2][3][1] Without the protein, the crystal structure would be too brittle to keep its form and the organic matrix is thought to have a role in deposition of calcium during the mineralization process.[4][5][6] The structure and composition of the avian eggshell serves to protect the egg against damage and microbial contamination, prevention of desiccation, regulation of gas and water exchange for the growing embryo, and provides calcium for embryogenesis. Eggshell formation requires gram amounts of calcium being deposited within hours, which must be supplied via the hen’s diet.[1]