Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. Naturally occurring rhodium is composed of only one isotope, 103Rh. It is one of the rarest and, with the price of about $80,000/kg in 2010, is the most expensive precious metal. Rhodium was discovered in 1803 by William Hyde Wollaston. It is found in platinum ores and is mostly used as a catalyst. Because of its rarity, rhodium is usually alloyed with platinum or palladium and applied in high-temperature and corrosion-resistive coatings. Rhodium detectors are used in nuclear reactors to measure the neutron flux level.