An eggshell is made of calcium carbonate, which is also the main ingredient in some antacids. The shell makes up 9-12 percent of an egg's total weight and contains pores that allow oxygen in and carbon dioxide and moisture out.
An egg white is made mainly of a protein called albumen, and also contains niacin (vitamin B3), riboflavin (vitamin B2), chlorine, magnesium, potassium, sodium, and sulfur, according to the Iowa Egg Council, an industry group. The white contains about 57 percent of an egg's protein.
The color of an egg yolk is determined by the hen's diet. The more yellow and orange plant pigments there are in the grain-fed to a hen, the more vibrant the color of the yolk will be.