Astatine

Astatine is the 85th element. Discovered in 1940 by Dale Corson, Kenneth McKenzie and Emilio Segre, it was once believed to be the rarest element on Earth. Astatine isn't the RAREST, but it is among the rare elements of Earth, as it is usually found in part of a larger element that is in radioactive decay. Only up to one gram of astatine is found in nature at a time.

Astatine is invisible with the naked eye, since a sample large enough to see would disintegrate from its own radioactivity. Because of this, it is estimated that there can only be TWENTY-EIGHT GRAMS OF ASTATINE ON EARTH AT A TIME. Astatine is an important element in nuclear medicine, but as it decays so quickly it must be used within a few hours of its production. It has been used instead of iodine in some procedures, safer as it has a shorter half-life.