Cleveite is a radioactive mineral containing uranium and found in Norway. It is an impure variety of uraninite, and has the composition UO2 with about 10% of the uranium substituted by rare earth elements. It was named after Swedish chemist Per Teodor Cleve.
Cleveite was the first known terrestrial source of helium, which is created by the alpha radiation of the uranium and then lies trapped (occluded) within the mineral. The first sample of helium was obtained by William Ramsay in 1895 when he treated a sample of the mineral with acid. Cleve and Abraham Langlet succeeded in isolating helium from cleveite at about the same time.
Yttrogummite is a variant of cleveite also found in Norway.