Astatine, with an estimated total mass of 25 grams on Earth, is the rarest natural element here. It is produced in some decay chains, its most stable isotope has a half-life of only a little above eight hours. Chemically, astatine is similar to iodine, but more metallic and inert than this. Despite its rarity and short life, it has an application. Nuclear medicine has preparations with tiny amounts of artificial astatine, made from bismuth, for inner irradiation. Astatine decays to polonium or to bismuth.