 Rhenium is one of the rarest elements in Earth 's crust with an average concentration of 1 ppb ; other sources quote the number of 0 @.@ 5 ppb making it the 77th most abundant element in Earth 's crust . Rhenium is probably not found free in nature ( its possible natural occurrence is uncertain ) , but occurs in amounts up to 0 @.@ 2 % in the mineral molybdenite ( which is primarily molybdenum disulfide ) , the major commercial source , although single molybdenite samples with up to 1 @.@ 88 % have been found . Chile has the world 's largest rhenium reserves , part of the copper ore deposits , and was the leading producer as of 2005 . It was only recently that the first rhenium mineral was found and described ( in 1994 ) , a rhenium sulfide mineral ( <unk> ) condensing from a fumarole on Russia 's <unk> volcano , <unk> island , in the Kuril Islands . <unk> discharges up to 20 – 60 kg rhenium per year mostly in the form of rhenium disulfide . Named <unk> , this rare mineral commands high prices among collectors . 
