 Rhenium is a chemical element with symbol Re and atomic number 75 . 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 . The free element has the third @-@ highest melting point and highest boiling point of any element , at 5 @,@ 869 K ( 10 @,@ 105 ° F ) . Rhenium resembles manganese and technetium chemically and is mainly obtained as a by @-@ product of the extraction and refinement of molybdenum and copper ores . Rhenium shows in its compounds a wide variety of oxidation states ranging from − 1 to + 7 . 
