The Australian half ounce platinum piece (abbreviated as 1/2 oz and designated with Pt for "Platinum") is a bullion coin format.
The Platinum Koala series was introduced by the Perth Mint in 1988 following the large success of Australia’s gold coins in the previous year, and the approval on 18 June 1987 by the Australian government of the minting of platinum and silver coins. It is the world's first platinum bullion coin (the American Platinum Eagle series started nine years later, in 1997). Regular production of the series was discontinued after 2000 due to low demand; after that time, there are only some commemorative issues.
The overall weight of the coins is slightly over half ounce, so as (accounting for the purity of the alloy) to have exactly 0.500 ounce of platinum content. | 
