Re: How are teeth similar to eggshells?

Both teeth and eggshells are made of stone-like minerals containing mostly 
calcium. Bird eggshells are made of calcium carbonate, while dental enamel is 
formed from calcium phosphate. Both of these materials are classified as 
COMPOSITES because they are actually not pure calcium carbonate or phosphate, 
but also contain additional components that are softer, and allow the 
mineral-like crystals to bond together into a rigid structure. The precise way 
the composite is organized, at the microscopic level, determines whether the 
material is hard and resiliant (like enamel) which is resistant to cracking, 
or hard and brittle like eggshell that cracks much more easily. To read more 
about how nature uses different materials, see if you can obtain a copy of the 
book--- _Life's Devices_, by Steven Vogel, 1988, Princeton University press--- 
from a local library. Or ask one of the librarians to help you find more 
information on the subject if the book isn't readily available.