What uranium-rich mineral was used by the Curies?

The uranium-rich mineral used by Marie and Pierre Curie was pitchblende, also known mineralogically as uraninite. The black, radioactive ore was an important source of uranium and, crucially, contained traces of radium and polonium.

The Curies investigated pitchblende after Henri Becquerel discovered that uranium compounds emitted penetrating radiation. They noticed that pitchblende was more radioactive than its uranium content could explain, suggesting that it contained unknown, even more radioactive elements. Processing large quantities of the ore eventually enabled them to announce the discovery of polonium in 1898 and radium later that year.

Pitchblende is mainly uranium dioxide, though natural specimens commonly contain oxidized uranium compounds and decay products such as lead, helium, and radium. The name refers to its dark appearance and the old German mining term for an ore that seemed to promise valuable metal but was difficult to exploit.

Torbernite, autunite, and carnotite are genuine uranium minerals, but they are not the canonical mineral associated with the Curies’ pioneering radium work. The Curies often processed pitchblende residues after uranium extraction because those residues were especially enriched in radium.