The essential mineral nutrients are classified into two groups: the principal elements calcium, phosphorus, sulfur, potassium, sodium, chlorine, and magnesium; and the trace and ultratrace elements iron, fluorine, zinc, silicon, copper, boron, selenium, iodine, manganese, molybdenum, chromium, cobalt, tin, vanadium, and nickel. These minerals perform a wide variety of functions serving as components of bones and teeth (calcium, phosphorus, fluorine); as components of cellular membranes (phosphorus); as high energy compounds (phosphorus); as components of proteins and amino acids (sulfur); in maintaining the appropriate pH and water volume of the organism (sodium, potassium, chlorine); in regulating metabolic rate (iodine); as components of (or cofactors for) enzymes (copper, zinc, selenium, molybdenum, manganese, iron, magnesium, calcium); in formation of hemoglobin (iron, cobalt, copper); in prevention of dental caries (fluorine); and in maintaining the appropriate level of muscle and nerve excitability (sodium, potassium, calcium, magnesium). Information is included on body content, daily requirement, effects of excess, deficiency or faulty utilization, modes of absorption and excretion, metabolic functions and modes of action, food sources, and toxicities.