U.S.Geological Survey (USGS): Rhodium

Statistics and Information: Naturally occurring platinum and platinum-rich alloys have been known for a long time. The Spaniards named the metal "platina," or little silver, when they first encountered it in Colombia. They regarded platinum as an unwanted impurity in the silver they were mining.

The catalytic properties of the six platinum group metals (PGM)– iridium, osmium, palladium, platinum, rhodium, and ruthenium – are outstanding. The chemical industry uses a significant amount of either platinum or a platinum-rhodium alloy catalyst in the form of gauze to catalyze the partial oxidation of ammonia to yield nitric oxide, which is the raw material for fertilizers, explosives, and nitric acid. Palladium, platinum, and rhodium have been used as oxidation catalyst in catalytic converters to treat automobile exhaust emissions.

U.S. Geological Survey, Mineral Commodity Summaries,January 2009