What Are the Components of an Egg Shell?

[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]

Egg shells are made of calcium carbonate

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

• [/size]
  
  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:
  
  
  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.