The Australian gold half gram coin is a mini-coin format occasionally used to complement issues in larger sizes. 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 have long-running bullion series of coins with different themes. As part of these, they sometimes issue a mini-version of the theme's annual design.
This coin is part of the long-running Australian Kangaroo bullion coin series by the Perth Mint, and is a "numismatic" issue with a one-year design. Due to its small size, its reverse represents only part of the design of the larger coins.
The Mint says about it:
This adorable kangaroo keepsake is also highly affordable and will make a beautiful gift or collectable. The kangaroo is a quintessential Australian icon. Perfectly adapted for the arid Australian outback and rural areas, kangaroos are herbivores and live on grass, plants, and shoots and obtain most of their water intake from the food they eat. | 
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