Important ores include hematite, magnetite, limonite, and siderite. Iron and its salts are consumed in the diet and through supplementation. The average iron content of a healthy adult is only about 4 grams and yet this relatively small quantity is vitally important. The majority of the remainder is storage iron which is found in the liver, spleen, bone marrow and muscle in the form of ferritin or hemosiderin. Additional minute quantities exist in the respiratory enzymes and in iron-binding protein of the plasma.
Iron is present in a variety of foods of both plant and animal origin.
In many foods there is a considerable variation in the value of iron content according to the soil and conditions in which the food is raised. Rich food sources for iron include meat, especially liver, egg yolk and pulses such as beans and peas. However, many other common foods such as green leafy vegetables, whole grain and enriched cereals, vegetables and fish are good sources of iron. In the United States many prepared foods such as bread, breakfast cereals and certain baby foods are artificially enriched with iron. An average American adult diet consisting of a variety of common foods bought at a grocery store or eaten in a restaurant or institution would normally contain about 15 milligrams of iron per day.