Cleveite

Cleveite is an impure radioactive variety of uraninite containing uranium and found in Norway. It 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 over time by alpha decay of the ...
Found on http://en.wikipedia.org/wiki/Cleveite

Cleveite

Cleveite is a uranium-containing mineral, of interest owing to the fact that when heated with dilute sulphuric acid it liberates considerable quantities of occluded helium. It was this property which first led to the discovery of the element helium.
Found on http://www.probertencyclopaedia.com/browse/HC.HTM