<Tr> <Td_colspan="2"> <Ul> <Li> view </Li> <Li> talk </Li> <Li> </Li> </Ul> references </Td> </Tr> <Ul> <Li> view </Li> <Li> talk </Li> <Li> </Li> </Ul> <P> Astatine is a radioactive chemical element with symbol At and atomic number 85 . It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements . All of astatine's isotopes are short - lived; the most stable is astatine - 210, with a half - life of 8.1 hours . A sample of the pure element has never been assembled, because any macroscopic specimen would be immediately vaporized by the heat of its own radioactivity . </P> <P> The bulk properties of astatine are not known with any certainty . Many of them have been estimated based on the element's position on the periodic table as a heavier analog of iodine, and a member of the halogens (the group of elements including fluorine, chlorine, bromine, and iodine). Astatine is likely to have a dark or lustrous appearance and may be a semiconductor or possibly a metal; it probably has a higher melting point than that of iodine . Chemically, several anionic species of astatine are known and most of its compounds resemble those of iodine . It also shows some metallic behavior, including being able to form a stable monatomic cation in aqueous solution (unlike the lighter halogens). </P>

What is the most rarest element on earth