Australia is one of the large issuers of bullion coins. Uniquely, there are two independent mints in the country 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. Their issues are normally in standard sizes (mostly based on the troy ounce), but sometimes they also issue coins in non-standard formats, such as this one
This coin is part of the Australian Wedge-tailed Eagle series by the Perth Mint, and the second design by John M. Mercanti (issued in 2016 and 2017 only).
The Mint says about it:
"The Perth Mint is delighted to present this incredible bi-metal coin featuring one of John M. Mercanti’s original designs in pure gold and silver. Each coin is struck from 1/2oz of 99.99% pure gold and 1/2oz of 99.9% pure silver in proof quality.
The coin’s pure gold centrepiece depicts an impressive Wedge-tailed Eagle perching on a tree branch. For this design, The Perth Mint commissioned American sculptor and engraver, John M. Mercanti, the 12th Chief Engraver of the U.S. Mint. John Mercanti created the reverse design of the American Silver Eagle bullion coin and has produced more coin and medal designs than any other employee in the history of the U.S. Mint."