The six platinum group metals (PGMs) occur together in nature alongside nickel and copper. Mineable deposits of PGMs are very rare, with annual production amounting to around 400 tonnes, several orders of magnitude lower than many common metals. Due to their economic values and higher quantities, platinum and palladium are the most important metals of the PGMs. The other four, rhodium, ruthenium, iridium and osmium, are mined as by-products of platinum and palladium.