wonderwomen22

http://antoine.frostburg.edu/chem/senese/101/consumer/faq/eggshell-composition.shtml

The main ingredient in eggshells is [|calcium carbonate] (the same brittle white stuff that chalk, limestone, cave stalactites, sea shells, coral, and pearls are made of). The shell itself is about 95% CaCO3 (which is also the main ingredient in sea shells). The remaining 5% includes calcium phosphate and magnesium carbonate and soluble and insoluble proteins.