In the earth's crust, rhenium occurs even less frequently than gold. In its pure state, rhenium is a very hard, brilliant metal, similar to platinum, and can only be formed at red heat. Its melting point, 3,186°C, is among the highest of all metals. It has a boiling point of 5,596°C and a density of 21.03 g/cm3. Due to these unique properties, rhenium is indispensable in many key industries such as aviation.