Shell Games

Let's start talking about the various parts of an egg from the outside in. The hard outer covering of the common chicken egg is, of course, called the shell. Eggshells contain 95% of the mineral calcium carbonate and 5% of protein. Calcium carbonate (CaCO₃) can also be found in other places - sea shells, pearls, and rocks such as limestone and marble.

In the supermarket, you will see eggs with both white and brown shells. There isn't any difference in the nutrition you get from either color. It's just that some breeds of chickens (such as the Leghorn) lay white eggs, and some (like the Delaware) lay brown eggs. There is actually a kind of South American chicken (the Araucana) that lays blue-green eggs!