The Australian 50 cent denomination was first introduced as a silver coin with decimalisation on 14 February 1966, but was changed in 1969 to its current specifications: a large dodecagonal (12-sided) copper-nickel coin; apart from the usual design featuring the Australian Coat of Arms (by Stuart Devlin) which has not been changed since its introduction, the denomination is also often used to issue circulating commemorative coins with various reverses. It is one of the heaviest coins in regular circulation in the world.
Apart from the circulating coinage, the Royal Australian Mint has an extensive program issuing 50 cent coins for collectors (Non-Circulating Legal Tender, or NCLT). Some of them - such as this one - are round, as reference to the original format of the denomination.
This coin was part of the 5-coin set Matserpieces in Silver 2000 - Coins of the 20th Century - Monarchs. The set depicts five monarchs whose effigies have circulated on Australian currency during the 20th Century. The set contains:
2 Dollars with Queen Victoria
20 Cents with King Edward VII
20 Cents with King George V
50 Cents with King George VI (this coin)
20 Cents with Queen Elizabeth II - Mary Gillick effigy
All of these coins have the Fourth Portrait of Queen Elizabeth II by Ian Rank Broadley) on the obverse - which also shows the value and denomination; on the other side, they have a historic obverse depicting one of the monarchs and carrying his/her legend, in Latin language as was the practice on pre-decimal coins. Thus, they have the curious appearance of having two obverses, although technically speaking the "historic" side is a commemorative reverse in this case.
Actual mintage of the set was 10,412 from an initially announced limit of 15,000.
The coins are made of 99.9% silver and were issued in Proof FDC grade only. No coins of this type were released into circulation.