Which metal is the most expensive?

Rhodium is generally the most expensive precious metal traded, at times reaching over 25,000 US dollars per ounce — far above gold. It is extremely rare, mostly recovered as a by-product of platinum and nickel mining, and its main use is in catalytic converters that clean vehicle exhaust, which makes its price highly sensitive to the car industry. Other members of the platinum group, such as palladium, iridium and platinum itself, are also very valuable. If radioactive and synthetic elements are included, substances like californium-252 cost tens of millions of dollars per gram, but these are laboratory products rather than tradable metals.