Rhenium

Rhenium was the last stable element to be discovered, in 1925, and at about one part per billion in the crust it is among the rarest; there is no rhenium ore, and essentially the entire world supply — perhaps 50 tonnes a year — is recovered as a by-product of roasting molybdenum concentrates from copper mines. Three percent of it in a nickel superalloy dramatically slows creep, which is what allows a single-crystal turbine blade to sit in a gas stream hotter than its own melting point and survive, cooled from within. The rest goes into platinum-rhenium catalysts that reform naphtha into high-octane gasoline. Rhenium also has the highest boiling point of any element, 5590 °C, edging out tungsten.