Uraninite named, was either unknown, impossible or not economically feasible). The mineral has been known at least since the 15th century from silver mines in the Ore Mountains, on the German/Czech border. The type locality is the historic mining and spa town known as Joachimsthal, the modern day Jáchymov, on the Czech side of the mountains, where F. E. Brückmann described the mineral in 1772. Pitchblende from the Johanngeorgenstadt deposit in Germany was used by M. Klaproth in 1789 to discover the element uranium. All uraninite minerals contain a small amount of radium as a radioactive decay product of uranium. Marie
Stephanie Horovitz radiochemistry. It predicted that lead resulting from the radioactive decay of uranium or thorium would have different atomic weights than typical lead. Early experimental data was not considered authoritative by analytical chemists. Hönigschmid had studied under leading expert Theodore Williams Richards at Harvard and his work in determining precise atomic weights was well respected. Horovitz isolated lead from uranium-rich pitchblende samples from the St. Joachmistal mine. Her gravimetric analysis to the thousandth of a gram proved that lead created from the radioactive decay of uranium had a lower atomic weight than typical lead. This was the first widely-accepted experimental proof