Mineral Resource of the Month: Iodine

by U.S. Geological Survey
Thursday, June 14, 2018

Désirée E. Polyak, a mineral commodity specialist for the U.S. Geological Survey, compiled the following information on iodine, an essential trace element vital to the production of thyroid hormones.

A man relaxes in the Galos Caves salt cave in Chicago, Ill. Sessions in the human-made cave, which was created with Black Sea iodine salt, are purported to help with medical issues ranging from sinus and respiratory problems to high blood pressure. Credit: Scott Olson/Getty Images

Although not abundant in quantity, iodine, a bluish-black lustrous solid, is found almost everywhere. It is present in animal tissue, food, plants, rocks, soils and water. Except for a few rare occasions, however, iodine almost never occurs independently in nature. Instead, iodine is usually combined with other elements, either in the form of inorganic salts or complex organic compounds.

For humans, iodine is an essential element that enables the thyroid gland to produce thyroid hormones. Both excessive iodine intake and iodine deficiency can cause a range of medical conditions, such as goiter, hyperthyroidism and hypothyroidism. Many countries, including the United States, mandate universal salt iodization (iodized salt) to help prevent these diseases.

In industry, iodine and its compounds are primarily used in colorants, medicine and photography. It is also used in animal feed, antiseptics, catalysts, food supplements, halogen lights, pharmaceuticals, starch detection and water purifying.

Iodine is only found in abundance in a few places, including mineral springs, seaweeds, sponges and corals, the underground waters from certain deep oil-well drilling, and the natural deposits of sodium nitrate, called caliche ore, found in the northern part of Chile. Underground brines in Japan and caliche ore deposits in Chile are the largest sources of iodine. Even in these deposits the proportion of iodine is small. The caliche ore, for example, has a typical iodine content of about 0.04 percent (400 parts per million).

Before the development of iodine extraction from caliche, seaweed, especially from off the coast of China, was an important source. Iodine is obtained as a byproduct in the processing of sodium alginate. Yearly output is dependent on the seaweed crop and harvest efficiencies, which are subject to environmental factors.

Three companies account for all U.S. production of iodine, mining it from deep well brines in northern Oklahoma. Historically, commercial iodine production also occurred in California, Louisiana and Michigan, but all of those sites have been abandoned for economic and/or environmental reasons.

For more information on iodine and other mineral resources, visit minerals.usgs.gov/minerals.


Chile and Japan lead the world in iodine production.

U.S. apparent consumption of iodine increased in 2007, as did imports. The three U.S. producers supplied 25 percent of the U.S. apparent consumption.

U.S. iodine consumption growth is strongest in the pharmaceutical and sanitation end-use markets.


French chemist Barnard Courtois discovered iodine in 1811.

Tincture of iodine is often included in emergency survival kits, used both to disinfect wounds and to sanitize surface drinking water.

In 1924, Morton Salt Company began distributing iodized salt throughout the United States.

The U.S. Recommended Daily Allowance of iodine for adults is 150 micrograms per day.

Only two ounces of potassium iodate, costing about $1.15, are required to iodize one ton of salt.

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