Discovered in: 1811

Discovered by: Bernard Courtois of France

Description: 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 also is used as a nutrient additive to table salt. Like carbon, nitrogen and phosphorous, iodine cycles through the biosphere.

Biological Rating: Critical for life processes in plants and animals.

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.

Percentage Amount in the Human Body: 0.00002 %

Obtained from: 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 also is obtained from seaweed.