Rhenium

Rhenium is a dense, silvery white metal that takes its name from the Latin, Rhenus, for the Rhine river. It was discovered in 1925 by Ida and Walter Noddack along with Otto Berg. (L. Rhenus: Rhine) Discovery of rhenium is generally attributed to Noddack, Tacke, and Berg, who announced in 1925 they had detected the element in platinum ore and columbite. They also found the element in gadolinite and molybdenite. By working up 660 kg of molybdenite in 1928 they were able to extract 1 g of rhenium.

Rhenium was another of the "missing" elements proposed by Mendeleev. The first sample was concentrated 100,000 fold from a gadolinium ore sample. Just enough was obtained for a spectroscopic study in which previously unseen lines were observed. The metal is acid resistant and has one of the highest melting points. But its scarcity (and therefore expense) makes practical use limited