MadSci Network: Cell Biology

Re: What is the molecular structure of a Chicken Eggshell-what makes it so strong?

Date: Tue Feb 23 14:22:01 1999
Posted By: Joe Regenstein, Faculty, Food Science, Cornell University
Area of science: Cell Biology
ID: 919616162.Cb

The cell of a chicken egg is made up of about 94 percent calcium carbonate 
(Ca(CO3)2), 1 percent magnesium carbonate, 1 percent calcium phosphate, and 
about 4 percent organic matter, mainly protein. The egg shell has pores 
through which air, moisture, and even bacteria can pass. The shell 
represents about 11 percent of the weight of an egg. The shell is made up 
of three parts -- the mammillary or inner layer is adjacent to the shell 
membranes and has a "knob" like appearance. The middle layer, the bulk of 
the shell is made up of small calcite crystals, mostly randomly arranged 
with the pores running through it. The cuticle or top layer is a thin film 
of protein that covers the egg when it is layed, but which drys up and 
flakes off over time. The organization of the shell (i.e., the crystals of 
calcite) provides a rigid structure that protects against breakage in 
certain directions. On the other hand a small tap in some directions will 
crack the shell.

The information about the shell was taken from the USDA's Egg Grading 

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