CALCIUM One Large egg provides 3% of the Reference Daily Intake (RDI) for calcium - most of which is contained in the yolk. Calcium's major role is in building and maintaining bones and teeth. It is also essential for many other body functions related to the blood, nerves and muscles. The eggshell is composed largely of calcium carbonate (about 94%) and contains about 2 grams of calcium. It also contains small percentages of magnesium carbonate and calcium phosphate. -see Nutrients, Shell, Reference Daily Intakes