“In 1898, Polish-French scientist Marie Sklodowska Curie discovered the radioactive element radium while experimenting with pitchblende, a common uranium ore. She had observed that this ore was more radioactive than refined uranium. This indicated that there must be another element, even more radioactive than uranium, mixed in with this ore.
During the years between 1899 and 1902, Marie Curie dissolved, filtered and repeatedly crystallized nearly three tons of pitchblende. The goal of that work was a refined sample of the element - the yield was about 0.1 gram. This was enough for spectroscopic examination, and to determine the exact atomic weight of radium. This discovery, along with the element polonium, earned her a second Nobel Prize in 1911.” From Today In Science History