What is an egg shell made of?

[Gonzolo]

Hard substances are rare in biology. Egg shells feel and crack like ceramics, but it probably has carbon in it. It's not like nails and horns is it (dry and dead cells right?)? Bone? Please help me understand hard biological materials.

[hitssquad]

Hard substances are rare in biology. Egg shells feel and crack like ceramics, but it probably has carbon in it.

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
-------------------------------------------------------------------------
Message: (http://www.google.com/search?q=egg+%22shell+is%22+%22calcium+carbonate%2 2)


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
Manual.

[Gonzolo]

It's (almost) chalk! Thanks.