The unbreakable shell of an egg is a mystery. Every time you crack open an egg, it seems to break in half or bend at a weird angle. What gives? The answer lies in the yolk and white of the egg. Its structure helps protect its contents from outside aggressors.
Eggs have one of the most robust shells among solid foods. That is because the eggshell contains calcium carbonate, the same chemical compound that makes up most sea shells, chalk, and limestone.
Proteins arrange calcium carbonate nanoparticles into ordered crystals, forming the calcite mineral that makes up the shell. The shell isn’t solid, though. It has thousands of tiny holes, on average about 9,000, that let gases move in and out.
The shell also has a thin layer called the bloom or cuticle on the outside. This layer helps keep bacteria and dust out.