Platinum coins are a form of currency. Platinum has an international currency symbol under ISO 4217 of XPT. The issues of legitimate platinum coins were initiated by Spain in Spanish-colonized America in the 18th century and continued by the Russian Empire in the 19th century. As a form of currency, these coins proved to be impractical: platinum resembles many less expensive metals, and, unlike the more malleable and ductile silver and gold, it is very difficult to work. Several commemorative coin sets have been issued starting from 1978 and became popular among coin collectors. The major platinum bullion coins include the American Platinum Eagle, the Canadian Platinum Maple Leaf, the Australian Platinum Koala, the Isle of Man Noble, the Chinese Platinum Panda and several series by the Soviet Union and later by the Russian Federation.