Francium was discovered by Marguerite Perey in France (from which the element takes its name) in 1939. It was the last element discovered in nature, rather than synthesized. Trace amounts found can be found in uranium and thorium ores, where the isotope francium-223 continually forms and decays, the other isotopes are entirely synthetic. The largest amount ever collected of any isotope was a cluster of about 10,000 atoms (of francium-210) created as an ultracold gas at Stony Brook in 1997.