53I Iodine

Year Discovered


Discovered By

Bernard Courtois of France

Biological Rating

Necessary for all life.


Named from the Greek word meaning “violet,” iodine is a shiny blue-black solid. Like other halogens, iodine is very reactive, although it is the least reactive of the group. Like arsenic, iodine sublimes directly from a solid to a purple vapor when it is heated. Iodine compounds are used as medicine and potassium iodide is used for a disinfectant. Silver iodide is used in photography and in cloud seeding. Iodine is also used as a nutrient additive to table salt. Like carbon, nitrogen and phosphorus, iodine cycles through the biosphere.

Biological Benefits

Iodine is an essential trace element to many species, including humans. It is a component of thyroid hormones. Lack of iodine will cause goiter, a thyroid deficiency disease. Iodine is believed to be the heaviest element required by humans.

Role in Life Processes

Critical for life processes in plants and animals.

Percentage Amount in the Human Body: 0.00002%


Minerals of iodine are uncommon—iodargyrite (silver iodide) and lautarite are two iodine-bearing minerals. Iodine is obtained mainly from seawater, old salt brines and salt wells, as well as nitrate deposits found in Chile. Some iodine is also obtained from seaweed.