The Australian Florin is a silver coin which was used in the Commonwealth of Australia prior to decimalisation. It has the same dimensions and composition as the British pre-decimal florin, from which it is derived (for a time, the coins circulated in parallel and were interchangeable in Australia - but not in the United Kingdom). A Florin is equal to two shillings, or 24 pence, or one tenth of a pound.
The reverse of this first type of Australian florin coins features the 1908 Coat of Arms; it became obsolete almost immediately, since Australia received a new Coat of Arms in 1912. In 1938, a new design superseded this one - featuring the new Coat of Arms.
No florin coins were issued into circulation in 1920. This was an experimental piece produced as part of a planned debasement of the silver alloy. The debasement, in the end, did not occur. There is a star above the date, which is designed to indicate that the silver in the coin had been debased below the then standard of sterling silver (0.925 fine). A similar pattern shilling was struck in 1919.
It is not clear if the silver in this pattern was actually debased, or if the only change was the star. Greg McDonald's "Australian Coins and Banknotes" catalogue lists the 1920 Florin as "Unissued circulation strike". Museums Victoria (which owns one of the specimens, and inherited the collection and archive of the Melbourne Mint) does not specify the composition.
According to Remick's Catalogue of British Commonwealth Coins 1649 - 1971, only four specimens are known. | 
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