The Australian five ounces gold piece (abbreviated as 5 oz and designated with Au for "gold") is a bullion coin format. Uniquely, in Australia there are two mints authorised to strike legal tender: the Royal Australian Mint (which also makes the country's circulating coinage) and the Perth Mint which only makes collector and bullion coins, as well as other bullion products.
Both mints endeavour to create coins with attractive designs, and to introduce new designs and themes often, in order to raise the numismatic value of the coins over the value of previous metal used.
This coin is part of the long-running Australian Kangaroo bullion coin series by the Perth Mint.
The mint says about it:
Symbolising Australia’s finest coin-making traditions, this superb Australian Kangaroo is struck from 5oz of 99.99% pure gold with a flawless proof finish.
Australia’s most famous marsupial, the kangaroo has appeared on The Perth Mint’s signature coin series since 1989. Featuring superbly observed portrayals of the iconic animal, the Australian Kangaroo Coin Series has a reputation for quality, purity and design that extends around the globe. | 
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