Rhodium is extremely hard and bright. Rhodium is primarily used in jewelry as a plating to give white gold extra shine. Rhodium is also used as an alloying agent for hardening platinum and palladium.
Rhodium has both a higher melting point and lower density than platinum. It is not attacked by acids and only dissolves in aqua regia. It is one of the most expensive precious metals.
Rhodium (From the Greek rhodon meaning "rose") was discovered in 1803 by William Hyde Wollaston soon after his discovery of palladium. The industrial extraction of rhodium is complex as the metal occurs in ores mixed with other metals such as palladium, silver, platinum, and gold.
Principal sources of this element are located in South Africa, in river sands of the Ural Mountains, in North America and South America. The main exporter of rhodium is South Africa (80%) followed by Russia. However, the annual world production of this element is only about 20 tons.
Physical Properties of Rhodium:
Melting point: 2237 degrees K
Crystal System: Face-centered cubic crystal
Hardness: 6.0 Mohs'
Color: bright white metallic
Luster: bright, shiny