Re: How are the eggs (chicken) hard shelled made and why?

The egg shell provides mechanical strength to the eggs. This protects the 
chick inside the egg and permits the parents to move (turn) the eggs and to 
sit on them. The shell is a porous material, mainly calcium carbonate. It 
covers the two membranes surrounding the egg white -- the inner and outer 
shell membranes -- these are the materials that provide the anti-microbial 
protection. The shell is created in the oviduct after all the other stages 
of the egg are assembled.