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 half gram gold mini-coin is part of the long-running Australian Kangaroo bullion coin series by the Perth Mint.
The Mint says about it:
Struck from 0.5g of precisely the same 99.99% pure gold we use to craft our most prestigious collectables and sought-after investment coins, this button-sized release is an affordable way to begin your gold coin collection, or gift some of the world’s most alluring precious metal.
Australia’s most recognised animal symbol, the kangaroo has been regularly portrayed on Australian coins, tokens and medallions since the 1850s. Honouring the historic precedent, The Perth Mint began crafting outstanding gold coins featuring annual designs of the famous marsupial in 1989. | 
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