About 95% of the eggshell is calcium carbonate, and the remaining 5% is a mix of other minerals, such as calcium phosphate and magnesium carbonate, as well as soluble and insoluble proteins. These components strongly influence the strength of the shell. A hen on a diet low in calcium or vitamin D, for example, lays eggs having thin, soft shells, or no shells at all, according to the American Egg Board (AEB), a group representing the egg industry.