What is the rarest metal in the Earth's crust?
Rhenium is a chemical element with symbol Re It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust. Discovered in 1908, rhenium was the second-last stable element to be discovered. It was named after the river Rhine in Europe.