Rhodium

William Hyde Wollaston found rhodium in 1803 in crude South American platinum and named it for the rose colour of its salts. It is vanishingly rare, at about 0.2 parts per billion in the crust, and world supply is roughly thirty tonnes a year, most of it from South Africa. Almost all of it goes into three-way catalytic converters, where rhodium performs the reduction half of the job, converting nitrogen oxides back to nitrogen — palladium and platinum can handle the oxidation of CO and hydrocarbons, but nothing matches rhodium on NOx. Tightening emissions limits and a supply shock drove the price to nearly 30000 dollars an ounce in early 2021, around fifteen times gold, which in turn drove a wave of catalytic converter thefts. Rhodium plating is also what gives white gold jewellery its bright, non-yellowing finish.