An eggshell is the outer covering of an egg. It is thin and brittle, and can be white or brown depending on the breed of the egg-laying animal. Eggshells are composed of calcium carbonate, which is the same material found in seashells, limestone, and chalk. They serve as a protective barrier for the developing embryo inside the egg and also help regulate the exchange of gases and moisture with the outside environment. Eggshells are often used for a variety of purposes such as gardening, crafting, and cooking.