Francium: The Elusive and Radioactive Element Francium, with the symbol Fr and atomic number 87, is a fascinating, yet challenging element to study due to its unique properties: Extreme Rarity: Francium is the second rarest naturally occurring element on Earth, even scarcer than astatine. Only about 30 grams exist at any given time, making it difficult to isolate and study … [Read more...] about Francium: The Mysteries Elusive and Radioactive Element