What are oysters made of?

Oysters are marine bivalves that are found in all oceans. They are made of two shells that are held together by a hinge. The shells are made of calcium carbonate, which is a mineral that is also found in chalk and limestone. The inside of the oyster shell is lined with a layer of nacre, which is also known as mother-of-pearl. Nacre is made of calcium carbonate and a protein called conchiolin. Oysters also have a soft body that is made up of various organs, including a heart, stomach, and gills.