Astatine's atomic number is 85 and its symbol is At. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of the 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. The sample contained in this cube is uranium autunite, which is about 50% uranium by weight. It is estimated that there are approximately 5 atoms of astatine for every 1 gram of uranium via nuclear decay. Given that we put about 2 grams of uranium autunite in each cube, you should have 0-5 atoms of astatine in your model at any given moment. These atoms will theoretically only last about 2.5 seconds each. The bulk properties of astatine are not known with certainty, but many of them have been estimated based on the element's position on the periodic table. Astatine is likely to have a dark or lustrous appearance and could be a semiconductor or possibly a metal. Named after the Greek word astériktos, meaning "unstable". Less than one gram is present in the Earth's crust at any given time. Neither the most stable isotope astatine-210, nor the medically useful astatine-211, occur naturally; they can only be produced synthetically. This display is contained within crystal clear Lucite acrylic.