Iodine is a chemical element that is essential to humans, but not easy to find in commercial quantities.

According to the latest edition of Encylopedia Britannica, it is a “non-metallic, nearly black crystalline solid that is used in medicine, in chemical syntheses, in the manufacture of dyes, in analytical chemistry, and in photography.” The advent of digital photography has dented one of its markets, but others have taken up the slack. Its compounds are used in CT scans and MRIs, as well as in the manufacture of high-tech LCDs.